Ain Shams University

Faculty of Engineering
Design and Production dep.

The Clocks

Presented By:
Mina Farid Fouad
Mina Samir Mosaad
Mina Samir Aziz
Mina Saleh Ayad
Mina Nabil Nasr
Mina Gad Seif
Stonehenge
Celestial bodies, the sun, moon,
planets, and stars have provided us
a reference for measuring the
passage of time throughout our
existence. Ancient civilizations
relied upon the apparent motion of
these bodies through the sky to
determine seasons, months, and
years.

Little is known about the details of

timekeeping in prehistoric eras,
however, records and artifacts that
are discovered show that in every
culture, people were preoccupied
with measuring and recording the passage of time. Ice-age hunters in
Europe over 20,000 years ago scratched lines and gouged holes in sticks
and bones, possibly counting the days between phases of the moon. Five
thousand years ago, Sumerians in the Tigris-Euphrates valley in today's
Iraq had a calendar that divided the year into 30-day months, divided the
day into 12 periods (each corresponding to 2 of our hours), and divided
these periods into 30 parts (each like 4 of our minutes). There are no
written records of the creating of Stonehenge, built over 4000 years ago in
England, but its alignments show its purposes apparently included the
determination of seasonal or celestial events, such as lunar eclipses,
solstices and so on.

The earliest Egyptian calendar was based on the moon's cycles, but later
the Egyptians realized that the "Dog Star" in Canis Major, which is now
called Sirius, rose next to the sun every 365 days, about when the annual
inundation of the Nile began. Based on this knowledge, they devised a
365-day calendar that seems to have begun in 4236 B.C., the earliest
recorded year in history.

In Babylonia, again in Iraq, a year of 12 alternating 29-day and 30-day

lunar months was observed before 2000 B.C., giving a 354-day year. In
contrast, the Mayans of Central America relied on not only the sun and
moon, but also the planet Venus, to establish 260-day and 365-day
calendars. This culture flourished from around 2000 B.C. until about 1500
A.D. They left celestial-cycle records indicating their belief that the creation
of the world occurred in 3113 B.C. Their calendars later became portions of
the great Aztec calendar stones. Other civilizations, including the modern
West, have adopted a 365-day solar calendar with a leap year occurring
every fourth year.
Sun Clock, Water Clock, Obelisk

Egyptian shadow clock with Obelisk:

Not until somewhat recently (that is, in terms of

human history) did people find a need for knowing
the time of day. As best we know, 5000 to 6000
years ago great civilizations in the Middle East and
North Africa initiated clock making as opposed to
calendar making. With their attendant bureaucracies
and formal religions, these cultures found a need to
organize their time more efficiently.

Sun Clock:

After the Sumerian culture was lost without passing on its knowledge, the
Egyptians were the next to formally divide their day into parts something
like our hours. Obelisks (slender, tapering, four-sided monuments) were
built as early as 3500 B.C. Their moving shadows formed a kind of sundial,
enabling citizens to partition the day into two parts by indicating noon.
They also showed the year's longest and shortest days when the shadow at
noon was the shortest or longest of the year. Later, markers added around
the base of the monument would indicate further time subdivisions.

Another Egyptian shadow clock or sundial, possibly the first portable

timepiece, came into use around 1500 B.C. to measure the passage of
"hours." This device divided a sunlit day into 10 parts plus two "twilight
hours" in the morning and evening. When the long stem with 5 variably
spaced marks was oriented east and west in the morning, an elevated
crossbar on the east end cast a moving shadow over the marks. At noon,
the device was turned in the opposite direction to measure the afternoon
"hours".

The merkhet, the oldest known astronomical tool, was an Egyptian

development of around 600 B.C. Two merkhets were used to establish a
north-south line by lining them up with the Pole Star. They could then be
used to mark off nighttime hours by determining when certain other stars
crossed the meridian.

In the quest for more year-round accuracy, sundials evolved from flat
horizontal or vertical plates to forms that were more elaborate. One version
was the hemispherical dial, a bowl-shaped depression cut into a block of
stone, carrying a central vertical gnomon (pointer) and scribed with sets of
hour lines for different seasons. The hemicycle, said to have been invented
about 300 B.C., removed the useless half of the hemisphere to give an
 appearance of a half-bowl cut into the edge of a squared block. By 30 B.C.,
Vitruvius could describe 13 different sundial styles in use in Greece, Asia
Minor, and Italy.

Elements of a Clock
Having described a variety of ways devised over the past few millennia to
mark the passage of time, it is instructive to define in broad terms what
constitutes a clock. All clocks must have two basic components:

A regular, constant or repetitive process or action to mark off

equal increments of time. Early examples of such processes
included movement of the sun across the sky, candles marked in
increments, oil lamps with marked reservoirs, sand glasses
("hourglasses"), and in the Orient, small stone or metal mazes filled
with incense that would burn at a certain pace.
A means of keeping track of the increments of time and displaying
the result. Our means of keeping track of time passage include the
position of clock hands and a digital time display.

The history of timekeeping is the story of the search for ever more
consistent actions or processes to regulate the rate of a clock.

Water Clock

Water clocks were among the earliest

timekeepers that did not depend on
the observation of celestial bodies.
One of the oldest was found in the
tomb of Amenhotep I, buried around
1500 B.C. Later named clepsydras
("water thief") by the Greeks, who
began using them about 325 B.C.,
these were stone vessels with sloping
sides that allowed water to drip at a
nearly constant rate from a small hole
near the bottom. Other clepsydras
were cylindrical or bowl-shaped containers designed to slowly fill with
water coming in at a constant rate. Markings on the inside surfaces
measured the passage of "hours" as the water level reached them. These
clocks were used to determine hours at night, but may have been used in
daylight as well. Another version consisted of a metal bowl with a hole in
the bottom; when placed in a container of water the bowl would fill and
sink in a certain time. These were still in use in North Africa this century.

More elaborate and impressive mechanized water clocks were developed

between 100 B.C. and 500 A.D. by Greek and Roman horologists and
astronomers. The added complexity was aimed at making the flow more
constant by regulating the pressure, and at providing fancier displays of
the passage of time. Some water clocks rang bells and gongs; others
opened doors and windows to show little figures of people, or moved
pointers, dials, and astrological models of the universe.

A Greek astronomer, Andronikos, supervised the construction of the Tower

of the Winds in Athens in the 1st century B.C. This octagonal structure
showed scholars and marketplace shoppers both sundials and mechanical
hour indicators. It featured a 24-hour mechanized clepsydra and indicators
for the eight winds from which the tower got its name, and it displayed the
seasons of the year and astrological dates and periods. The Romans also
developed mechanized clepsydras, though their complexity accomplished
little improvement over simpler methods for determining the passage of
time.

In the Far East, mechanized astronomical/astrological clock making

developed from 200 to 1300 A.D. third-century Chinese clepsydras drove
various mechanisms that illustrated astronomical phenomena. One of the
most elaborate clock towers was built by Su Sung and his associates in
1088 A.D. Su Sung's mechanism incorporated a water-driven escapement
invented about 725 A.D. The Su
Sung clock tower, over 30 feet
tall, possessed a bronze power-
driven armillary sphere for
observations, an automatically
rotating celestial globe, and five
front panels with doors that
permitted the viewing of changing
manikins which rang bells or
gongs, and held tablets indicating
the hour or other special times of
the day.

Since the rate of flow of water is

very difficult to control accurately,
a clock based on that flow could
never achieve excellent accuracy.
People were naturally led to other
approaches.
Mechanical Pendulum Clock and Quartz Clock

Pendulum used to keep time:

In Europe during most of the Middle Ages (roughly 500 to 1500

A.D.), technological advancement was at a virtual standstill.
Sundial styles evolved, but didn't move far from ancient
Egyptian principles.

During these times, simple sundials placed above doorways

were used to identify midday and four "tides" of the sunlit day.
By the 10th Century, several types of pocket sundials were
used. One English model identified tides and even compensated
for seasonal changes of the sun's altitude.

Then, in the early-to-mid-14th century, large mechanical clocks

began to appear in the towers of several large Italian cities.
There is no evidence or record of the working models preceding these
public clocks that were weight-driven and regulated by a verge-and-foliot
escapement. Verge-and-foliot mechanisms reigned for more than 300
years with variations in the shape of the foliot. All had the same basic
problem: the period of oscillation of this escapement depended heavily on
the amount of driving force and the amount of friction in the drive. Like
water flow, the rate was difficult to regulate.

Another advance was the invention of spring-powered clocks between 1500

and 1510 by Peter Heinlein, a German locksmith from Nuremberg.
Replacing the heavy drive weights permitted smaller (and portable) clocks
and watches. Heinlein nicknamed his clocks "Nuremberg Eggs". Although
they slowed down as the mainspring unwound, they were popular among
wealthy individuals due to their size and the fact that they could be put on
a shelf or table instead of hanging from the wall. They were the first
portable timepieces. However, they only had an hour hand, minute hands
did not appear until 1670, and there was no glass protection. Glass over
the face of the watch did not come about until the 17th century. Still,
Heinlein’s advances in design were precursors to truly accurate
timekeeping.

Accurate Mechanical Clock

In 1656, Christian Huygens, a Dutch scientist, made the first pendulum

clock, regulated by a mechanism with a "natural" period of oscillation.
Although Galileo Galilee, sometimes credited with inventing the pendulum,
studied its motion as early as 1582, Galileo's design for a clock was not
built before his death. Huygens' pendulum clock had an error of less than 1
minute a day, the first time such accuracy had been achieved. His later
refinements reduced his clock's errors to less than 10 seconds a day.

Around 1675, Huygens developed the balance wheel and spring assembly,
still found in some of today's wrist watches. This improvement allowed
17th century watches to keep time to 10 minutes a day. And in London in
1671 William Clement began building clocks with the new "anchor" or
"recoil" escapement, a substantial improvement over the verge because it
interferes less with the motion of the pendulum.

In 1721, George Graham improved the pendulum clock's accuracy to 1

second a day by compensating for changes in the pendulum's length due to
temperature variations. John Harrison, a carpenter and self-taught clock-
maker, refined Graham's temperature compensation techniques and added
new methods of reducing friction. By 1761, he had built a marine
chronometer with a spring and balance wheel escapement that won the
British government's 1714 prize (of over $2,000,000 in today's currency)
offered for a means of determining longitude to within one-half degree
after a voyage to the West Indies. It kept time on board a rolling ship to
about one-fifth of a second a day, nearly as well as a pendulum clock could
do on land, and 10 times better than required.

Over the next century refinements led in 1889 to Siegmund Riefler's clock
with a nearly free pendulum, which attained an accuracy of a hundredth of
a second a day and became the standard in many astronomical
observatories. A true free-pendulum principle was introduced by R. J. Rudd
about 1898, stimulating development of several free-pendulum clocks. One
of the most famous, the W. H. Shortt clock, was demonstrated in 1921.
The Shortt clock almost immediately replaced Riefler's clock as a supreme
timekeeper in many observatories. This clock consists of two pendulums,
one a slave and the other a master. The slave pendulum gives the master
pendulum the gentle pushes needed to maintain its motion, and also drives
the clock's hands. This allows the master pendulum to remain free from
mechanical tasks that would disturb its regularity.

Quartz Clock

The Short clock was replaced as the standard by quartz crystal clocks in
the 1930s and 1940s, improving timekeeping performance far beyond that
of pendulum and balance-wheel escapements.

Quartz clock operation is based on the piezoelectric property of quartz

crystals. If you apply an electric field to the crystal, it changes its shape,
and if you squeeze it or bend it, it generates an electric field. When put in a
suitable electronic circuit, this interaction between mechanical stress and
electric field causes the crystal to vibrate and generate a constant
 frequency electric signal that can be used to operate an electronic clock
display.

Quartz crystal clocks were better because they had no gears or

escapements to disturb their regular frequency. Even so, they still relied on
a mechanical vibration whose frequency depended critically on the crystal's
size and shape. Thus, no two crystals can be precisely alike, with exactly
the same frequency. Such quartz clocks continue to dominate the market
in numbers because their performance is excellent and they are
inexpensive. But the timekeeping performance of quartz clocks has been
substantially surpassed by atomic clocks.

Atomic Clock and Time Standard

Scientists had long realized that atoms (and molecules) have resonances;
each chemical element and compound absorbs and emits electromagnetic
radiation at its own characteristic frequencies. These resonances are
inherently stable over time and space. An atom of hydrogen or cesium here
today is exactly like one a million years ago or in another galaxy. Here was
a potential "pendulum" with a reproducible rate that could form the basis
for more accurate clocks.

The development of radar and extremely high frequency radio

communications in the 1930s and 1940s made possible the generation of
the kind of electromagnetic waves (microwaves) needed to interact with
the atoms. Research aimed at developing an atomic clock focused first on
microwave resonances in the ammonia molecule. In 1949, NIST built the
first atomic clock, which was based on ammonia. However, its performance
wasn't much better than existing standards, and attention shifted almost
immediately to more-promising, atomic-beam devices based on cesium.

In 1957, NIST completed its first cesium atomic beam device, and soon
after a second NIST unit was built for comparison testing. By 1960, cesium
standards had been refined enough to be incorporated into the official
timekeeping system of NIST.

In 1967, the cesium atom's natural frequency was formally recognized as

the new international unit of time: the second was defined as exactly
9,192,631,770 oscillations or cycles of the cesium atom's resonant
frequency replacing the old second that was defined in terms of the earth's
motions. The second quickly became the physical quantity most accurately
measured by scientists. The best primary cesium standards now keep time
to about one-millionth of a second per year.

Much of modern life has come to depend on precise time. The day is long
past when we could get by with a timepiece accurate to the nearest quarter
hour. Transportation, communication, manufacturing, electric power and
many other technologies have become dependent on super-accurate
clocks. Scientific research and the demands of modern technology continue
to drive our search for ever more accurate clocks. The next generation of
cesium time standards is presently under development at NIST's Boulder
laboratory and other laboratories around the world.

Atomic Clock, Time Scale, and Time Zone

In the 1840s, a Greenwich standard time for all of England, Scotland, and
Wales was established, replacing several "local time" systems. The Royal
Greenwich Observatory was the focal point for this development because it
had played such a key role in marine navigation based upon accurate
timekeeping. Greenwich Mean Time (GMT) subsequently evolved as the
official time reference for the world
and served that purpose until 1972.

The United States established the

U.S. Naval Observatory (USNO) in
1830 to cooperate with the Royal
Greenwich Observatory and other
world observatories in determining
time based on astronomical
observations. The early
timekeeping of these observatories
was still driven by navigation.
Timekeeping had to reflect changes
in the earth's rotation rate;
otherwise navigators would make
errors. Thus, the USNO was
charged with providing time linked
to "earth" time, and other services,
including almanacs, necessary for
sea and air navigation.

With the advent of highly accurate

atomic clocks, scientists and
technologists recognized the
inadequacy of timekeeping based
on the motion of the earth which
fluctuates in rate by a few thousandths of a second a day. The redefinition
of the second in 1967 had provided an excellent reference for more
accurate measurement of time intervals, but attempts to couple GMT
(based on the earth's motion) and this new definition proved to be highly
unsatisfactory. A compromise time scale was eventually devised, and on
January 1, 1972, the new Coordinated Universal Time (UTC) became
effective internationally.

UTC runs at the rate of the atomic clocks, but when the difference between
this atomic time and one based on the earth approaches one second, a
one-second adjustment (a "leap second") is made in UTC. The National
Institute of Standards and Technology's clock systems and other atomic
clocks located in more than 25 countries now contribute data to the
international UTC scale coordinated in Paris by the International Bureau of
Weights and Measures (BIPM). An evolution in timekeeping responsibility
from the observatories of the world to the measurement standards
laboratories has naturally accompanied this change from "earth" time to
"atomic" time. But there is still a needed coupling, the leap second,
between the two.

The World's Time Zones

Time zones did not become necessary in the United States until trains
made it possible to travel hundreds of miles in a day. Until the 1860s most
cities relied upon their own local "sun" time, but this time changed by
approximately one minute for every 12 1/2 miles traveled east or west.
The problem of keeping track of over 300 local times was overcome by
establishing railroad time zones. Standard time zones were first invented
by Scottish-Canadian, railroad engineer, Sir Sandford Fleming in 1878, and
universally accepted in 1884. However, until 1883 most railway companies
relied on some 100 different, but consistent, time zones.

That year, the United States was divided into four time zones roughly
centered on the 75th, 90th, 105th, and 120th meridians. At noon, on
November 18, 1883, telegraph lines transmitted GMT time to major cities
where authorities adjusted their clocks to their zone's proper time.

On November 1, 1884, the International Meridian Conference in

Washington, DC, applied the same procedure to zones all around the world.
The 24 standard meridians, every 15° east and west of 0° at Greenwich,
England, were designated the centers of the zones. The international
dateline was drawn to generally follow the 180° meridian in the Pacific
Ocean. Because some countries, islands and states do not want to be
divided into several zones, the zones' boundaries tend to wander
considerably from straight north-south lines.
Types of Clocks:
There are many types of clocks the most important types of them are:

THE ALARM CLOCK

History of the Alarm Clock:

The first mechanical clocks were made in the 14th century, and
were large monumental clocks. Household clocks were in use by 1620 and
some of them had alarm mechanisms. The alarm is simple in concept,
typically having a cam that rotates every 12 hours. It has a notch into
which a lever can fall, releasing a train of gears that drives a hammer,
which repeatedly hits a bell until it runs down or is shut off (many alarms
have no shutoff control).

The earliest alarm clock I found reference to is a German iron wall clock
with a bronze bell, probably made in Nuremberg in the 15th century. This
clock is 19 inches tall and of open framework construction. It needed to
hang high on the wall to make room for the driving weight to fall. Other
alarm clocks from the 1500's are in existence. See “The Clockwork
Universe, German Clocks and Automata 1550 - 1650,” Maurice and Mayr,
1980, Smithsonian, Neale Watson Academic Publications, New York.

The book “Early English Clocks” by Dawson, Drover and Parkes, Antique
Collectors Club, 1982, documents some early alarm clocks. An example is a
lantern clock ca. 1620 that has an alarm set disc on front of the dial. One
long case (grandfather) clock ca. 1690 is documented, as is a 30 hour
hanging timepiece alarm by Joseph Knibb.

English clockmakers immigrated to the United States in the 18th century

and no doubt carried the idea of the alarm clock with them. It has been
said that Levi Hutchins of Concord, New Hampshire invented the first alarm
clock in 1787. He may have made an early American alarm clock, but his
clock was predated by the German and English ones mentioned above.

Simon Willard of Grafton, Massachusetts, made alarm time timepieces

sometimes called “lighthouse clocks” in the 1820's. Some of the American
wooden works shelf clocks of the 1820's - 30's have alarms, as do many
brass movement shelf clocks after 1840.

Seth Thomas Clock Company was granted a patent in 1876 for a small
bedside alarm clock. This may have been the first clock of this type, or
perhaps other makers were working on this idea at the same time. In the
late 1870's, small alarm clocks became popular, and the major US clock
companies started making them, followed by the German clock companies.
The predecessor of Westclox was founded in 1885 with an improved
method of small clock construction.

Westclox introduced the Chime Alarm in 1931. This clock was advertised
with the slogan “First he whispers, and then he shouts.”

The Westclox Moonbeam was introduced in 1949. This clock's alarm flashes
a light on and off, and then a buzzer sounds. Westclox now sells an
excellent reproduction of the Moonbeam.

General Electric-Telechron first marketed a snooze alarm in 1956. The first

Westclox Drowse (snooze) electric alarms were sold in 1959 and could be
set for five (5) or ten (10) minutes snooze time.

Modern Clock Trivia

In 1577, Jost Burgi invented the minute hand. Burgi's invention was part of
a clock made for Tycho Brahe, an astronomer who needed an accurate
clock for his stargazing.

In 1656, the pendulum was invented by Christian Huygens, making clocks

more accurate.

In 1504, the first portable (but not very accurate) timepiece was invented
in Nuremberg, Germany by Peter Heinlein. The first reported person to
actually wear a watch on the wrist was the French mathematician and
philosopher, Blaise Pascal (1623-1662). With a piece of string, he attached
his pocket watch to his wrist.

The word 'clock' comes from the French word "cloche" meaning bell. The
Latin for bell is glocio, the Saxon is clugga and the German is glocke.

Sir Sanford Fleming invented standard time in 1878.

An early prototype of the alarm clock was invented by the Greeks around
250 BC. The Greeks built a water clock where the raising waters would
both keep time and eventually hit a mechanical bird that triggered an
alarming whistle. The first mechanical alarm clock was invented by Levi
Hutchins of Concord, New Hampshire, in 1787. However, the ringing bell
alarm on his clock could ring only at 4 am. On October 24, 1876 a
mechanical wind-up alarm clock that could be set for any time was
patented (#183,725) by Seth E Thomas.

Swiss John Harwood invented the self-winding watch in 1923.

The mechanical components of the alarm clock
 THE Watch

A watch

A watch is a small portable clock that

displays the time and sometimes the
day, date, month and year. In modern
times they are usually worn on the
wrist with a watch-strap (made of e.g.
leather (often synthetic), metal, or
nylon), although before the 20th
century most were pocket watches,
which had covers and were carried
separately, often in a pocket, and hooked to a watch chain.

Current watches are often digital watches, using a piezoelectric crystal,

usually quartz, as an oscillator (see quartz clock).

Mechanical timepieces are still used, usually powered by a spring wound

regularly by the user, e.g. a stem winder. The invention of "Automatic" or
"Self-Winding" watches allowed for a constant winding without special
action from the wearer: it works by an eccentric weight, called a winding
rotor, that rotates to the movement of the wearer's body. The back-and-
forth motion of the winding rotor couples to a ratchet to automatically wind
the watch.

Watches may be collectible; they are often made of precious metals, and
can be considered an article of jewelry.

Types of watch
1) Pocket clock

The earliest need for portability in time keeping was navigation and
mapping in the 15th century. The latitude could be measured by looking at
the stars, but the only way a ship could measure its longitude was by
comparing timezones; by comparing the midday time of the local longitude
to a European meridian (usually Paris or Greenwich), a sailor could know
how far he was from home. However, the process was notoriously
unreliable until the introduction of John Harrison's chronometer. For that
reason, most maps from the 15th century to c.1800 have precise latitudes
but distorted longitudes.

The first reasonably accurate mechanical clocks measured time with

weighted pendulums, which are useless at sea or in watches. The invention
of a spring mechanism was crucial for portable clocks. In Tudor England,
the development of "pocket-clockes" was enabled through the development
of reliable springs and escapement mechanisms, which allowed
clockmakers to compress a timekeeping device into a small, portable
compartment. In 1524, Peter Henlein created the first pocket watch[1][2].
It is rumoured that Henry VIII (the portrait of Henry VIII at this link shows
the medallion thought to be the back of his watch) had a pocket clock
which he kept on a chain around his neck. However, these watches only
had an hour hand - a minute hand would have been useless considering
the inaccuracy of the watch mechanism. Eventually, miniaturization of
these spring-based designs allowed for accurate portable timepieces which
worked well even at sea. Aaron Lufkin Dennison founded Waltham Watch
Company in 1850, which was the pioneer of the industrial manufacturing
by interchangeable parts, the American System of Watch Manufacturing.

2) Wrist watch

Breitling Navitimer Montbrillant, a typical

pilot watch. Quantum on hand, day of
the week, month, slide rule, chronometer
certified.

The wristwatch was invented by Patek

Philippe at the end of the 19th century.
It was however considered a woman's
accessory. It was not until the beginning
of the 20th century that the Brazilian
inventor Alberto Santos-Dumont, who
had difficulty checking the time while in
his first aircraft (Dumont was working on
the invention of the aeroplane), asked
his friend Louis Cartier for a watch he
could use more easily. Cartier gave him a leather-band wristwatch from
which Dumont never separated. Being a popular figure in Paris, Cartier was
soon able to sell these watches to other men. During the First World War,
officers in all armies soon discovered that in battlefield situations, quickly
glancing at a watch on their wrist were far more convenient than fumbling
in their jacket pockets for an old-fashioned pocket watch. In addition, as
increasing numbers of officers were killed in the early stages of the war,
NCOs promoted to replace them often did not have pocket watches
(traditionally a middle-class item out of the reach of ordinary working-class
soldiers), and so relied on the army to provide them with timekeepers. As
the scale of battles increased, artillery and infantry officers were required
to synchronize watches in order to conduct attacks at precise moments,
whilst artillery officers were in need of a large number of accurate
timekeepers for rangefinding and gunnery. Army contractors began to
issue reliable, cheap, mass-produced wristwatches which were ideal for
these purposes. When the war ended, demobilized European and American
officers were allowed to keep their wristwatches, helping to popularize the
items amongst middle-class Western civilian culture. Today, many
Westerners wear watches on their wrist, a direct result of the First World
War.

3) Complicated watch

A complicated watch has one or more functionalities beyond basic time-

keeping capabilities; such functionality is called a complication. Two
popular complications are the chronograph complication, which is the
ability of the watch movement to function as a stopwatch, and the
moonphase complication, which is a display of the lunar phase. Among
watch enthusiasts, complicated watches are especially collectible.

4) Chronograph and chronometer

The similar-sounding terms chronograph and chronometer are often

confused, although they mean altogether different things. A chronograph is
a type of complication, as explained under the heading "Complicated
Watch." A chronometer is a watch or clock whose movement has been
tested and certified to operate within a certain standard of accuracy by the
COSC (Contrôle Officiel Suisse des Chronomètres). The concepts are
different but not mutually exclusive; a watch can be a chronograph, a
chronometer, both, or neither.

5) Electromechanical watch

The first use of electrical power in watches was as a source of energy to

replace the mainspring, and therefore to remove the need for winding. The
first battery-powered watch, the Hamilton Electric 500, was released in
1957 by the Hamilton Watch Company of Lancaster, Pennsylvania.

6) Quartz analog watch

The quartz analog watch is an electronic watch that uses a piezoelectric

quartz crystal as its timing element, coupled to a mechanical movement
that drives the hands. The first prototypes were made by the CEH research
laboratory in Switzerland in 1962. The first quartz watch to enter
production was the Seiko 35 SQ Astron, which appeared in 1969. There are
also several variations of the quartz watch as to what actually powers the
movement. There are solar powered, kinetically powered, battery powered
and other less common power sources. Solar powered quartz watches are
powered by available light. Kinetic powered quartz watches make use of
the motion of the wearer's arm turning a rotating weight, which in turn,
turns a generator to supply power. A seldom used power source is
temperature difference between the wearer's arm and the surrounding
environment (as applied in the Citizen Eco Drive Thermo). The most
common power source is the battery. Watch batteries come in many forms,
the most common of which are silver oxide and lithium.

7) Digital watch

Cheaper electronics permitted the popularization of the digital watch (an

electronic watch with a numerical, rather than analog, display) in the
second half of the 20th century. They were seen as the great new thing.
Douglas Adams, in the introduction of his novel The Hitchhiker's Guide to
the Galaxy, would say that humans were 'so amazingly primitive that they
still think digital watches are a pretty neat idea'.

The first digital watch, a Pulsar prototype in 1970, was developed jointly by
Hamilton Watch Company and Electro-Data. A retail version of the Pulsar
was put on sale in 1972. It had a red light-emitting diode (LED) display.
LED displays were soon superseded by liquid crystal displays (LCDs), which
used less battery power. The first LCD watch with a six-digit LCD was the
1973 Seiko 06LC, although various forms of early LCD watches with a four-
digit display were marketed as early as 1972 including the 1972 Gruen
Teletime LCD Watch [3], [4].

In addition to the function of a timepiece, digital watches can have

additional functions like a chronograph, calculator, video game, etc.

Digital watches have not replaced analog watches, despite their greater
reliability and lower cost. In fact, because digital watches are so cheap,
analog watches are often worn as status symbols. For others, analog
watches are just easier to read.

8) Fashionable watch

At the end of the 20th century, Swiss watch makers were seeing their sales
go down as analog clocks were considered obsolete. They joined forces
with designers from many countries to reinvent the Swiss watch.

The result was that they could considerably reduce the pieces and
production time of an analog watch. In fact it was so cheap that if a watch
broke it would be cheaper to throw it away and buy a new one than to
repair it. They founded the Swiss Watch company (Swatch) and called
graphic designers to redesign a new annual collection.

This is often used as a case study in design schools to demonstrate the

commercial potential of industrial and graphic design.

9) Advanced watch

In 1990 radio controlled wristwatches or as they are sometimes called

"atomic watches" reached the market. These wristwatches normally receive
a radio signal from one of the national atomic clock facilities around the
world, for example the National Institute of Standards and Technology
located in Colorado in the United States. This radio signal tells the
wristwatch exactly what time it is, in theory precise to a fraction of a
nanosecond. It will also reset itself when daylight saving time changes.
Similar signals are broadcast from Rugby, England and Frankfurt,
Germany. In recent years, mass production has meant that atomic watches
have become as cheap as quartz watches, though market share still
remains small as interest from big manufacturers is limited.

Other technological enhancements to wristwatches have been explored but

most of them remained unnoticed. In 2005 for example, a company has
put into market an alarm wristwatch with an accelerometer inside that
monitors the user's sleep and rings during one of his almost-awake phases.

A number of functionalities non directly related to time have also been

inserted into watches. As miniaturized electronics become cheaper,
watches have been developed containing calculators, video games, digital
cameras, keydrives, GPS receivers and cellular phones. In the early 1980s
Seiko marketed a watch with a television receiver in it, although at the
time television receivers were too bulky to fit in a wristwatch, and the
actual receiver and its power source were in a book-sized box with a cable
that ran to the wristwatch. In the early 2000s, a self-contained wristwatch
television receiver came on the market, with a strong enough power source
to provide one hour of viewing.

These watches have not had sustained long-term sales success. As well as
awkward user interfaces due to the tiny screens and buttons possible in a
wearable package, and in some cases short battery life, the functionality
available has not generally proven sufficiently compelling to attract buyers.
Such watches have also had the reputation as ugly and thus mainly geek
toys. Now with the ubiquity of the mobile phone in many countries, which
have bigger screens, buttons, and batteries, interest in incorporating extra
functionality in watches seems to have declined.

Several companies have however attempted to develop a computer

contained in a WristWatch (see also wearable computer). As of 2005, the
only programmable computer watches to have made it to market are the
Seiko Ruputer, the Matsucom onHand, and the Fossil, Inc. WristPDA,
although many digital watches come with extremely sophisticated data
management software built in.

The Atomic clock

Atomic clock Chip-Scale Atomic Clock Unveiled by NIST

An atomic clock is a type of clock that uses an atomic resonance frequency

standard as its counter. Early atomic clocks were masers with attached
equipment. Today’s best atomic frequency standards (or clocks) are based
on more advanced physics involving cold atoms and atomic fountains.
National standards agencies maintain an accuracy of 10-9 seconds per day,
and a precision equal to the frequency of the radio transmitter pumping the
maser. The clocks maintain a continuous and stable time scale,
International Atomic Time (TAI). For civil time, another time scale is
disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI,
but synchronized with the passing of day and night based on astronomical
observations.

The first atomic clock was built in 1949 at the U.S. National Bureau of
Standards. The first accurate atomic clock, based on the transition of the
caesium-133 atom, was built by Louis Essen in 1955 at the National
Physical Laboratory in the UK. This led to the internationally agreed
definition of the second being based on atomic time.

In August 2004, NIST scientists demonstrated a chip-scaled atomic clock.

According to the researchers, the clock was believed to be one hundredth
the size of any other. It was also claimed that it requires just 75 mW,
making it suitable for battery-driven applications.
Modern radio clocks are referenced to atomic clocks, and provide a way of
getting high-quality atomic-derived time over a wide area using
inexpensive equipment; however, radio clocks are not appropriate for high-
precision, scientific work.

How they work

Frequency reference masers use glowing chambers of ionized gas, most

often caesium, because caesium is the element used in the official
international definition of the second.

Since 1967, the International System of Units (SI) has defined the second
as 9,192,631,770 cycles of the radiation which corresponds to the
transition between two energy levels of the ground state of the Caesium-
133 atom. This definition makes the caesium oscillator (often called an
atomic clock) the primary standard for time and frequency measurements
(see caesium standard). Other physical quantities, like the volt and metre,
rely on the definition of the second as part of their own definitions.

The core of the atomic clock is a microwave cavity containing the ionized
gas, a tunable microwave radio oscillator, and a feedback loop which is
used to adjust the oscillator to the exact frequency of the absorption
characteristic defined by the behavior of the individual atoms.

The microwave transmitter fills the chamber with a standing wave of radio
waves. When the radio frequency matches the hyperfine transition
frequency of caesium, the caesium atoms absorb the radio waves and emit
light. The radio waves make the electrons move farther from their nuclei.
When the electrons are attracted back closer by the opposite charge of the
nucleus, the electrons wiggle before they settle down in their new location.
This moving charge causes the light, which is a wave of alternating
electricity and magnetism.

A photocell looks at the light. When the light gets dimmer because the
frequency of the excitation has drifted from the true resonance frequency,
electronics between the photocell and radio transmitter adjusts the
frequency of the radio transmitter.

This adjustment process is where most of the work and complexity of the
clock lies. The adjustment tries to eliminate unwanted side-effects, such as
frequencies from other electron transitions, distortions in quantum fields
and temperature effects in the mechanisms. For example, the radio wave’s
frequency could be deliberately cycled sinusoidally up and down to
generate a modulated signal at the photocell. The photocell’s signal can
then be demodulated to apply feedback to control long-term drift in the
radio frequency. In this way, the ultra-precise quantum-mechanical
 properties of the atomic transition frequency of the caesium can be used to
tune the microwave oscillator to the same frequency (except for a small
amount of experimental error). In practice, the feedback and monitoring
mechanism is much more complex than described above. When a clock is
first turned on, it takes a while for it to settle down before it can be
trusted.

A counter counts the waves made by the radio transmitter. A computer

reads the counter, and does math to convert the number to something that
looks like a digital clock, or a radio wave that is transmitted. Of course, the
real clock is the original mechanism of cavity, oscillator and feedback loop
that maintains the frequency standard on which the clock is based.

A number of other atomic clock schemes are in use for other purposes.
Rubidium clocks are prized for their low cost, small size (commercial
standards are as small as 400 cm3), and short term stability. They are used
in many commercial, portable and aerospace applications. Hydrogen
masers (often manufactured in Russia) have superior short term stability to
other standards, but lower long term accuracy.

Often, one standard is used to fix another. For example, some commercial
applications use a Rubidium standard slaved to a GPS receiver. This
achieves excellent short term accuracy, with long term accuracy equal to
(and traceable to) the U.S. national time standards.

The lifetime of a standard is an important practical issue. Modern Rubidium

standard tubes last more than ten years, and can cost as little as $50 US.
Caesium reference tubes suitable for national standards currently last
about seven years, and cost about $35,000 US. Hydrogen standards have
an unlimited lifetime.

Research
Most research focuses on way to make the clocks smaller, cheaper, more
accurate, and more reliable. These goals usually conflict.

A lot of research currently focuses on various sorts of ion traps.

Theoretically, a single ion suspended electromagnetically could be observed
for very long periods, increasing the accuracy of the clock, while also
reducing its size and power consumption.

In practice, single-ion clocks have poor short term accuracy because the
ion moves so much. Current research uses laser cooling of ions, with
optical resonators to increase the short term stability of the driving optics.
Much of the difficulty is related to eliminating temperature and mechanical
noise effects in the resonators and lasers. No laser has achieved wide use.
The result is that the ion trap is very small, but the supporting equipment
is still large.

Some researchers developed clocks with different geometries of ion traps,

as well. Linear clouds of ions usually have better short term accuracy than
single ions. There are trade-offs.

The best developed systems use Mercury ions. Some researchers

experiment with other ions. A particular isotope of Ytterbium has a
particularly precise resonant frequency in one of its hyperfine transitions.
Strontium has a hyperfine transition that is not as precise, but can be
driven by solid-state lasers. This might permit a very inexpensive, long-
lasting compact clock.

AND THERE IS A LOT OF OTHER TYPES OF CLOCKS AS :

Ogee clock
Nuclear clock
Long case clock ......etc.

From the early sundials, to the modern day atomic clocks, clocks have had
very little impact on the environment as they mostly depend on electricity
and burn no fuel.
Clocks have significantly led to an increase in productivity as they helped
regulate working hours and measure things such as machining times and
machine speeds that would greatly help in the automation of many
manufacturing processes and thus increase not only the productivity but
the quality of products.
As to the effect that clocks have had on our civilization, there can be no
doubt that they’ve introduced a lot of concepts into our lives: most
obviously, the concept of time. To be able to conceive of time as a
succession of events and as a measurable quantity was a milestone of
human civilization and helped spark a lot of scientific discoveries later. But
more importantly clocks have helped the advancement of life in the Ancient
Times. Having an objective standard with which to measure time, men
could communicate more easily, document events more accurately and
measure time rates, speeds, etc… Thus was born a science like mechanics
for example.
Socially, the clocks affect our daily life, because they keep us aware of
what little time we have to accomplish what we set out to do; and in an
age like ours, where time is everything, it’s not so strange that clocks are
so vitally important that the French poet Baudelaire has written a poem
about his fear of the clock!