If you don't already have DSWorld DSWorldfrom NGS you may want to consider downloading it soon. NGS has just added a geoid accuracy mapping function that will allow you to asses the accuracy of GEOID12A in any area of the country. If you already have it just go to the tool bar, select "Tools" and then "Update Program" and you get the new map added under the "Plot" option on the toolbar.
A very good tool to let you know how well you may be able to determine NAVD 88 heights from GPS. Also a great tool to let you know where adding GPS on an existing NAVD 88 bench mark by using OPUS-DB will help improve the next model. This is in addition to the other great functions that will plot existing control against Google Earth as well as to provide an easy method to submit digital images of marks found, updating scaled bench mark positions with hand-held GPS values as well as text recovery info. You can also access a webinar detailing the use of DSWorld from the NGS Online Learning Resources page -- http://www.ngs.noaa.gov/corbin/online_learning.shtml
Thanks for that info. Took me a while to figure out your user name meant...but I get it now.
I had some time this AM to look at DSWORLD. Very good implementation. I had not looked at it in a few years, since an early version. Definitely something I will be using a lot more.
Thanks, Dave