Every time a ship’s course is laid or changed, or its position noted,
the navigator must make and apply calculations to correct the errors
caused by variation of the earth’s magnetic fields, and deviation due
to local conditions about the ship. Mistakes are frequently made in
applying the correction factors by applying them to the wrong side. An
error is thus introduced, which in magnitude is twice the correction
factor. Instances are reported of ships being 200 miles out of their
courses as a result.
The Gyro-Compass requires no corrections since it is undisturbed by
variations or any local magnetic conditions. The reading indicated
by the Sperry Gyro-Compass is not approximate—it is absolutely and
immediately correct. It is not necessary to correct the course every
few hours for variation—the navigator is freed from the necessity of
making calculations.
[Illustration]