I read from NOAA that NAD83 and WGS84 are "navigationally equivalent"
NOAA uses the North American Datum of 1983 (NAD 83) for all of its charts. This datum is navigationally equivalent to the World Geodetic System of 1984 (WGS 84).
I am not familiar with this concept. Could some one explain how the two datums are different, and how are they equivalent in terms of navigation?