The vertical control datum established for vertical control surveying in the Unites States of America based upon the General Adjustment of the North American Datum of 1988. It replaces the National Geodetic Vertical Datum (NGVD) of 1929
United Nations Asian and Pacific Training Centre for Information and Communication Technology for Development (UN-APCICT/ESCAP), Everyday ICT terms for Policymakers and Government Officers, Incheon City, Republic of Korea 2011. https://www.google.com.kw/url?sa=t&rct=j&q=&esrc=s &source=web&cd=2&cad=rja&uact=8&ved=0CCIQFjAB&url= http%3A%2F%2Fwww.unapcict.org%2Fecohub%2Fdirectory -of-ict-for-development-ictd-training-institutions -in-the-asia-pacific-and-everyday-ict-terms-for-po licymakers-and-government-officers%2Fat_download%2 Fattachment2&ei=pwXtVIu8KYr1UtSQgKgM&usg=AFQjCNHPi jupJgWDFU_3o6451VYBUmyEqg&sig2=ToEEwxvBri8GkOVOftK XVA, (Info and Commun Tech - Amer) {255}