I edited the entry to be more specific about the difference from NGVD29. I welcome comments about anything I said wrong or confusing.
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My nitpicks, without knowledge of (or concern about) who authored what:
1. Use of the definite article ("the") before "NAVD88." While it would be appropriate to use "the" when spelling out the datum title, using it before their initialization is awkward and inconsistent with spoken usage.
2. Use of "underground" to modify "geoid." The geoid is the geoid, regardless of whether it's underground or not. There may not be many places in which it's above ground, but they do exist (e.g. Death Valley), so the modifier is both inappropriate and unnecessary.
3. Similarly, in the description of Helmert orthometric height, use of the phrase "based on then-available measurements" to modify "modeled local gravity" is confusing. I think it would be preferable to omit the modifier, but if the intent is to put the reader on notice that gravity modeling has improved markedly since NAVD88 was defined, the a more complete description of the situation would be helpful.
Nitpicking aside: kudos to you, Bill, for taking the time to improve the article.
Thanks. I've tried to incorporate those suggestions.
The last paragraph contains a confusing grammatical issue with the comparison of the relative elevations between the two datums.
It's a good cursory overview, but does not get into great depth on the topic.
I would suggest mentioning the local distortions in NGVD can exceed 20cm. Brian Shaw from the NGS sent me the following GIS image file that shows the VERTCON solutions at each pixel. It's pretty cool to see how it fluctuates normally. It would be better if they identified the ares where VERTCON fails to produce a valid solution within two centimeters. https://www.box.com/s/k17e5o4gqm6rbwfga661
I would consider mentioning the fact that a change in the datum is a fairly great ordeal for those who use datums.
I hope you had fun with the wiki.
