RAF issue Aircraft Clock, 6A/4833
Introduction
1. The Mk.5A, elapsed time, dashboard clock (Reference 6A/4833} has been designed to fulfil the requirement for an eight-day, self-starting, jewelled lever movement with normal time hour and minute hands together with a centre-seconds sweep hand and subsidiary off-set hand completing one revolution in fifteen minutes. The main dial therefore is divided into twelve equal 5 minute divisions with the smaller subsidiary dial having fifteen equal divisions. Both dials have Arabic numbers; at 12, 3 and 6-o'clock on the main dial and 15, 5 and 10-minutes on the smaller dial. The dial markings and hands are coated with a fluorescent material.
2. In addition to its normal time function, time of trip computations and elapsed time readings, over short periods, can be evaluated. The elapsed time action is chronographic since the centre- seconds hand is accurate to within one-fifth of a second.
DESCRIPTION
4. The clock movement and elapsed time mechanism are mounted on the front portion of a two-part cast metal case with a rubber gasket interposed between the two portions for sealing purposes. The separate portions are secured by means of two special nuts and bolts together with two small ch/hd. screws. Internal threads in each bolt provide a means of securing the clock to the aircraft dashboard.
14. Situated in the rear of the case is a screwed cap which, when removed, discloses the regulator lever reading against a graduated scale. The scale is rnarked in four divisions on both sides of a zero with a plus sign at one end, for advance, and a minus sign at the other, for retard.
OPERATION
15. When fully wound this clock should operate over a seven day period at the end of which rewinding, by means of the knob, is necessary. The elapsed time mechanism may be used for any situation demanding, up to, fifteen minute time checks. Total time of trip requirements may be recorded by setting, the normal time, hour and, minute hands to 12-o'clock and pushing in the winding and hand setting knob at take-off.
INSTALLATION
16. This instrument is secured to the aircraft dashboard by two 4 B.A. screws fitting into the insert threads of the special bolts.
17. When the Mk.5A clock replaces the 5 A.C.A. (Reference 6A/2089), Mk.4 (Reference 6A/2197) and Mk.4B (Reference 6A/2958) clocks, it is necessary to cut clearance holes in the dashboard for the winding knob and elapsed time operating knob.
18. When the Mk.5A clock replaces the V.308 (Reference 6A/3517), it is necessary to use an adapter plate (Reference 6A/2639). Clearance holes should be cut in the adapter plate for the \vinding knob and elapsed time operating knob.