North American Vertical Datum

Started in 1850’s, first phase completed in 1929
Thousands of points across the US and Canada were related to MSL and adjusted, The new defined MSL defined a new datum called: National Geodetic Vertical Datum of 1929, or (NGVD29)
Due to earth’s crust shifting and changes in MSL, new adjustment was done, more points were added (total of 1.3 million) which resulted in (NAVD88).
Shifts are larger in the west, 1.5 m in the Rocky Mountain Area.
Must mention which datum.