How to find Compass Error by Horizontal angle and Transit bearing.

Two of the methods of determining compass error by terrestrial observations are discussed below.
  • Error by Horizontal angle.
The compass bearings of three suitable terrestrial objects are taken in quick succession while the ship remains on a heading.Difference between two bearings is the horizontal angle between them.Two position circles drawn would intersect at a point forming the fix.This position is plotted in the chart and the true bearings of the objects are read off from there. These bearings are compared with the observed compass bearings and error determined.
  • Error by transit bearing
The bearing of Leading lights are observed through the gyro repeater and the true bearing of the line joining them from charts is compared and error is determined.

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