RAF issue Aircraft Clock, 6A/7804
Introduction
1. The time of flight clock, Ref. No. 6A/7804, is provided
to indicate time of flight between intermediate points, total flying time on
a flight which involves intermediate stops and in addition its normal function
as a conventional 12-hour time of day clock.
Leading particulars
2. Leading particulars are as follows:-
(1) 8-day self-starting mechanism.
(2) 12-hour rotation of time of day hands.
(3) 12-hour time of flight mechanism.
(4) Independant resetting of time of day without
disturbing time of flight hands.
(5) Tropicalized to allow for humidity and temperature changes.
(6) Mechanism fitted into standard S.A.E. case.
DESCRIPTION
3. This clock is of the conventional 8-day self-starting mechanism incorporating a 12-hour main dial with time of day hands, a subsidiary 12-hour dial (bottom centre) which registers time of flight. A second subsidiary dial (top centre) is provided as an AM/PM indicator, which is driven by the time of day mechanism, thus indicating the time of day on a 24-hour basis. All figures, markings and hands are white against a matt black back-ground. The AM scale (top half) of the 24-hour dial takes the form of two semi-circular concentric rings, the PM scale (lower half) is a semi-circular solid ring. A centre sweep second hand beats to one-fifth of a second.
4. The clock is fitted with a high grade movement, having 23 jewels, a balance assembly of high quality, and a Brequet overcoil hairspring and the complete mechanism is accommodated in a S.A.E. standard type case with 4BA stiff nuts integral with the case to facilitate flange mounting.
5. The time of flight shown on the 12-hour subsidiary dial is controlled by a three-pressure action press-button switch located at the 6 o'clock position. This switch operates in conjunction with an indicator disc visible through a window in the main dial at the 3 o'clock position. A black disc appearing in the window indicates that the time of day hands are functioning; a white disc indicates that the time of day hands are stopped or at zero.
6. The clock is wound by a friction-loaded winding button located at the 4 o'clock position. A friction-loaded overwind device incorporated in the winding button, ensures that the main spring cannot be broken, nor the winding mechanism damaged as the result of overwinding.
OPERATION
7. To wind the clock, turn the winding button in a clockwise direction. A friction-loaded drive prevents overwinding and possible damage.
Resetting time of day hands
8. To reset time of day hands, pull out the winding button. This action stops the clock and automatically returns the centre sweep second hand to zero, thus enabling the clock to be set in agreement with an outside time signal. The time of day hands and AM/PM scale may be adjusted to the desired time without disturbing the time of flight recording. The action of depressing the winding button on receipt of the time signal automatically restarts the clock.
Time of Flight
9. To reset the time of flight scale proceed as follows:-
(1) Pressing the push-button (6 o'clock position)
with black disc appearing in the window (3 o'clock position)indicates that
the hands are functioning and time of flight is being recorded on the subsidiary
dial.
(2) Pressing the push-button again with the white
disc appearing indicates that time of flight is stopped.
(3) A third pressure on the push-button returns
the time of flight hands to zero and the white disc will still appear in the
window.