Compass Check with pre-calculated Azimuth Angles
With the data contained in the manuals used for Celestial Navigation,
it is also a trivial matter to check the compass with the calculated
bearing to some celestial body, even well away from any land marks
and in a strong unknown current.
It is not possible to do this with GPS, nor any other instrumentation
The only way to truly check the compass at sea is with celestial techniques.
The simplest technique to achieve this, is derived from the
Rise and Set Times of celestial objects.
From the Sight Reduction Tables not only the LHA at local rise or set time
is determined but also the Azimuth for the corresponding object.
The Azimuth is the bearing to this object.
At the moment of rising or setting, the ships (true) course can be
changed such that the vessel heads exactly to the object on the horizon.
The true course is the calculated Azimuth and this can be compared to
the course read from the compass.
The deviation on this course can be recorded and corrected.