The requirements of navigation entering or leaving harbour or in narrow waters are exacting, and a very accurate position is usually essential. For this reason it is believed that inertial techniques should be applied in the first instance only to ocean navigation as, although the system will give the ship's position continually, the accuracy will be of the order of one mile.

The latitude and vertical references are absolute, but the longitude reference is relative to a known starting point. Besides position, an inertial system can also provide course, sidereal time and roll and pitch and, by comparison of successive positions, course and speed made good, and leeway. Furthermore the system could be used to feed position into an automatic plotting table, with a chart of suitable scale superimposed, so that the vessel's geographical location would be visible at a glance.