Gyrocompasses were first successfully developed at the beginning of the 20th century as a solution to the problems of magnetic variation and deviation that are inherent in magnetic compasses. They use the properties of spinning gyroscopes which keep the compass pointing in a fixed direction, usually Earth’s true north.

This master compass contains the gyroscopes that from the heart of the system and which would be transmitted to repeaters throughout the vessel. It also has a card on top, which is graduated in degrees (0-360 by 1 degree) and in points, with a fleur-de-lys at north. A red lubber line is painted onto a plastic mount protruding over the degree scale. The maker’s name is marked on the card as well as on labels on the side of the unit. There is also an inspection label from Tokyo Keiki Co. Ltd. There is also a latitude corrector on the front of the unit.