RAF issue Aircraft Clock, 6A/8464
Introduction
1. The general purpose aircraft clock, Pt. No. N.L.7510A, is of the 8-day type, capable of maintaining its accuracy for 7 days after being fully wound. It has a small. Type 2 S.A.E. case and weighs approximately 6 oz.
DESCRIPTION
2. A 12-hour conventional dial with a centre seconds hand shows the time of day. All figures, markings and hands are white on a matt black background. The case is of light alloy fitted with two integral 6/32 U.N.C. stiff nuts for mounting purposes.
3. A two-position, extended winding button is situated at 7-30 o'clock. The extended button facilitates winding or resetting of the hands when the clock is mounted behind certain aircraft instrument panels. No friction overwind device is incorporated, but the winding mechanism is designed to provide a strong recoil at full wind to minimize the risk of overwinding with subsequent damage to the mainspring and the winding mechanism.
4. The 15 jewel movement incorporates a temperature compensated balance assembly and a Breguet overcoil hairspring. The balance compensates for changes in temperature which might affect the moment of inertia of the balance and the modulus of elasticity of the balance spring. The overcoil is provided to maintain a constant centre of gravity.
5. Resetting of the time of day is accomplished by pulling out and turning the winding button in either direction. This action does not stop the clock or interfere with the seconds hand. After resetting, the button is returned to the normal position.