The Timer was a small diecast box containing a mains transformer, printed circuit board, selector switches and a 'Sonalert' tone generator.
The circuit used TTL logic to provide a interval clock counted from the 50Hz
mains.This was divided by 50 to give 1pps which was divided by 6 to give 10ppm.
This in turn was used in two ways.
a)divided by 10 to give 1pulse every minute and further divided by 2 to give 1 pulse every 2 minute
b) divided by 2 to give 1 pulse every 30 seconds
The output would turn on the sonalert for five seconds. Then after that period a relay would turn on whose contacts would cause the radar console display circuitry to stop updating via a connection into the data sockets on the right hand side of the WF3 console.
The box had a mains ON/OFF switch to disable the function during target acquistion and a reset button to synchronise the timing with the stop watch the observer would have started on balloon release.
Some nine years later a modification was added to fit a volume control on the tone generator for the comfort of observers!