How large is the North American Datum (NAD) 27 to NAD 83 shift?
Generally, for the conterminous United States, the North American Datum (NAD) shift amounts to about 210 meters. This shift occurs because of the change in shape of the spheroid used to define the datum. The GRS 80 spheroid (used for NAD 83) is shorter at the Equator and longer at the poles than the Clarke 1866 spheroid (which is used for NAD 27). The map collar says to move the projection just a few meters. The shift referenced in the map collar applies only to the LAT, LONG graticule on the map.