To determine the position of. a ship with hyperbolic position systems, the minimim requirement is two position lines. However, because of the frequent occurrence of lane slips, it is necessary to observe at least three patterns to be able to control the observations. This redundant observation makes it possible to compute an estimation of the standard deviation of the standard error ellipse of the position. Furthermore, the best estimate and position are obtained by an adjustment. In the adjustment, one should introduce the effect of the correlation between the patterns. The adjustment, testing, and computation of the precision of the position are described. Some interesting geometrical features of the error figure of the observed lanes are derived.
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