RAF issue Aircraft Clock, 6A/8460
INTRODUCTION
1. The clock, Type N.L.7510-A (Ref. No. 6A/8460), is a general-purpose,
8-day, aircraft type, capable of maintaining accuracy for 7 days after being
fully wound. It has a small, Type 2, S.A.E. case and weighs approximately six
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 re-setting 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. Re-setting of the hands is accomplished by the pulling out and turning of the winding button in either direction. This action does not stop the clock or interfere with the seconds hand. Afterwards, the button returns to the normal position.
INSTALLATION
6. The clock is secured to the aircraft instrument panel by two 6/32 U.N.C. screws on a P.C.D. of 2.625 in.