This diving compass is brand new. These compasses were produced between 1960 and 1970's. This one has a very low productionnumber. so it's from the early 60's.
The compass is used to work out direction under water up to 50 meters \\ 164 feet. It can also be used on the surface during the day or night.
(this is all translated from a manual).
‘Compass KHM consists of the three main parts: body (4), card (3) and base (7). The compass body is a truncated cone made of transparent plastic. The bottom part of the cone is joined to the base. Scale (8) is engraved on the side surface of the body. There is 10? between marks and 30? between digits. Two hands are engraved on top of the body parallel to the line 0 – 180?. Two trackers are installed there as well: subject tracker (9) and eye tracker (2). In the middle of the base a column with a pin is fixed. The compass card rests on it. The compass card is made of the same plastic as the body. The card has two magnets placed parallel to each other. A hand is engraved on top of the card. Marks, hands, trackers on the compass body and hands on the card are covered with fluorescent paint that make it possible to use compass in darkness.’
Fig. 51. Wrist magnetic compass:
1 – circle to establish compass’ horizontal position;
2 - eye tracker; 3 – card; 4 – body; 5 – bars for the strap; 6 – index;
7 – base; 8 – scale; 9 – object tracker.
‘To minimise card pressure, pin friction and stop it vibrating, the body of the compass is filled with 50% glycol solution or 43% ethanol solution. However, there is still a small air bubble left (diameter 8 –10 mm). The bubble is necessary to stop pressure mounting in the body when the liquid expands. It also shows the horizontal position of the compass. When the compass is in horizontal position, the bubble is inside the circle (1) that is drawn on compass body.’
‘The compass base is a brass ring that encircles the body. There is index (6) on the base and two bars (5) used to attach the strap. The strap is used to secure the compass on a diver’s hand. The body of the compass can be easily turned in the base so that any mark can be aligned with the index. Such alignment is useful so that a diver does not have to remember a set direction under water.'
'To move under water or on land according to the set azimuth, its corresponding mark needs to be aligned with the index on the base. The compass needs to be in horizontal position and needs to be rotated in horizontal plane until the card hands are parallel to the body hands. The direction of the movement is decided from the index on the base.’