Cetus GPS is the Swiss Army Knife of GPS tracking and field data collection.

“As a surveyor, you have vast opportunities. You can map the world’s terrain. Explore new oil sources. Investigate crime scenes. Take charge as a CEO. Appear in court as an expert witness…” […]

‘This process is designed to provide the datum shift between the NAVD 88 and NGVD 29 vertical datums at a specified geographic position’

old (2001) slideshow with some good information on NGVD, &c.