RAF issue Aircraft Clock, 6A/2197
Description
1. The Mk. 4 aircraft clock (Ref. No. 6A/2197) is a conventional 8-day movement. When installed, the only visible parts are the face, the winding knob and 1/8 in. rim around the cover glass.
2. This type of clock has a seven-jewel lever movement fitted with either a Breguet or flat hairspring. The dial is graduated into 12 hours corresponding with one revolution of the hour hand. One revolution of the minute band equals one hour, and one revolution of the centre-seconds hand equals one minute. At the back of the case is a cover screw, marked ADJ, which gives access to the index. the latter being engraved AR-FS for normal method of regulation.
3. Hand setting is carried out by a pull-out snap-action knob situated at 6 o'clock. The clock, which is of American design of 2.25 in. diameter, is fitted with an English movement. The weight of the clock is 8 oz approximately.
Note...
Adapter plates (Ref. No. 6A/1060) are available for use with Mk. 4 clocks. These provide interchangeability with Mk. 2 clocks.
4. The Mk. 4B aircraft clock (Ref. No. 6A/2958) differs from the Mk. 4 clock in that the winding knob is at the bottom left-hand corner and not in the 6 o'clock.