Vickers range clock

The clockwork motor drove the pointer at a constant rate determined by a control on the right hand side of the device.

Thus the clock could be set to the initial range to a ship, or corrections could be made to update the reading without disturbing the mechanism.

In such cases, the operators of the clock would periodically alter the range rate in discrete increments as conditions suggested.

Variable speed was obtained using a rotating metal disc driving a rubber wheel resting against it.

The workaround adopted was to adjust the rate quickly and in a discrete manner, accepting that the generated ranges would deviate moderately from the desired continuous hyperbolic curves that predominated in use.

[5] A small aperture on the dial would reveal a visual tell-tale which indicate that the clock's spring required winding.