Often times the modeler or the user needs to convert the vertical datum from system to another system. The most popular vertical datums are NGVD (National Geodetic Vertical datum) and NAVD (North American Vertical Datum). NAVD is the latest vertical datum which started in 1988 where as NGVD is often referred as NGVD 29.
There is an online tool which allows the user to convert between / from the datum.
The link is
http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert_con.prl
There is an online tool which allows the user to convert between / from the datum.
The link is
http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert_con.prl