You may also want to spend a few minutes with several YouTube videos on datums I did for the Florida GNSS Users Group a few years ago, all designed for those relatively new to geodetic surfaces and datums. -- https://www.youtube.com/channel/UCG69vYuN1Q61fWKiXffzo9A/videos
My long experience with many GPS users is that they often relabel NAD 83 as WGS 84 because they have been told they are the same -- THEY ARE NOT.
That's been my experience as well. Surveyors do it more than they should, but IMO environmental/resources folks tend to do it the most.
Beware the geodetic dataset labeled as simply "NAD83" or "WGS84" with no realization or epoch tag, and no metadata concerning collection or processing methodology.
Thank you StlSurveyor - it's been an amazing ride. I completely agree with Rover83's comment. As the use of GPS/GNSS has exploded (and will continue even more so) and requirements for higher degrees of geospatial integrity become the norm, far too many users have received their training in the fundamentals of geodesy/datums from whomever they bought the equipment from and they seldom know much on those topics and/or how it's realized as part of the U.S. National Spatial Reference System.
Adding to the good information already posted,I add the following screen captures. They show the geoid-ellipsoid separation using the GEOID18, USGG2012 and EGM08 geoid models. I also include a geoid height calculation using the tool at the UNAVCO site which should not be used.
Natural Resources Canada’s site is:
These tools yield heights (meters)of:
GEOID18 = -27.468 NGS
USGG12 = -27.555 NGS
EGM08 = -27.544 NRC (Canada)
UNAVCO = -14.371 said to be based on NGA’s EGM96
Another hopefully useful graphic from Penn State taken from GPS for Land Surveyors: