GB1265218A - - Google Patents

Abstract

1,265,218. Determining compass deviation. M. W. G. WEBSTER. Oct.26, 1970 [Aug. 4, 1969], No.38921/69. Heading G1F. An instrument for determining the deviation of a compass comprises a bearing plate J resting on a disc F and having one scale P for indicating a magnetic bearing and a second scale Q for indicating a relative bearing, an alidade K carrying a foresight L and a backsight M and supported on the bearing plate J such that it can rotate therewith about a pivot on the disc F, and a deviation plate R mounted on the disc F and having a short scale for determining West, East, and zero deviations. The disc F is supported horizontally on a block G having screws H resting in vertical slots of brackets C hinged to a base A. The sights L, M may fold down on to the alidade, which is of a transparent plastics material. In use, to determine the deviation of a ship's compass, the magnetic bearing of a distant object is determined from a chart and the alidade K is set and locked to the bearing plate J by a locking knob O so that its centre line V is aligned with this bearing on scale P. The bearing plate is turned till sights L, M are aligned with the object. With the ship headed in the required direction for adjustment of the compass, the steering compass is read and against this course, on scale P, is read the deviation on the deviation plate scale. The compass deviation on a subsequent course may be checked using the relative bearing scale Q and a distant object of known magnetic bearing.