The quality of the old reference systems varies, and system irregularities have created problems for some user groups. The problems have increased in line with the increase in the quality of the positioning systems. As the positioning accuracy when using new satellite systems can exceed the quality of the old reference systems, the Norwegian Mapping Authority decided to introduce a new satellite-based reference system in Norwegian waters from 1993.
WGS-84
World Geodetic System (WGS-84) replaced ED-50 as the official horizontal reference system at sea. This is a worldwide international geodetic reference system without the major irregularities associated with the former systems. Positions from GPS-based systems can be used directly in charts with WGS-84 graticule.
New nautical charts have WGS-84 graticule, while reprints of older charts use their existing graticule. All charts since 1986 have a field stating the offset between ED-50, alternatively NGO-48, and WGS-84. This difference will depend on the position, but the change is so slow that it can be assumed to remain constant within a sheet in the Main Chart Series. The offset between ED-50 and WGS-84 will typically be in the order of 100 metres. On charts with Norwegian Datum, the difference between the chart graticule and WGS-84 can reach 4-500 metres. With such a large difference between the graticules, it will be very important that the navigator takes this into consideration.