The Type III azimuth circle which has been a service stand-by for many years, plays an important part in navigation and is so well known that no description is considered necessary. Although sufficiently rugged to withstand ordinary use, accidental knocks or misuse will cause derangement. When out of adjustment the fault is difficult to determine and rectify with the facilities found on board ship. An error in the circle fittings affecting azimuths, affects the course laid by the amount of the error. As an example of this relation the experience of a certain ship is given. This ship while on a long voyage had a consistent, unaccountable set of about ten miles a day. As day after day elapsed with a set of approximately the same amount, it was suspected that the azimuth circle was out of adjustment. Comparison with other circles developed the fact that none of them agreed. Later when there was an opportunity to have the circle checked it was found to be out a degree and a half, which error almost exactly accounted for the set experienced.
Adjustment of the Type III Azimuth Circle
By Captain F. L. Oliver, U. S. Navy