Fixed Survey Meter

[1] The instrument was designed and built by the Atomic Weapons Establishment at Aldermaston as a replacement for the Radiac Survey Meter No 2 which could only be used above ground.

The Royal Observer Corps’ need was for an instrument that could be read from inside the protected environment on the underground post.

The delicate instruments were kept at the group controls in an air conditioned and de-humidified storage room and only issued to posts during Transition To War.

Posts were provided with a dummy FSM trainer, known as the FSMT, that was identical in every way to the operational instrument except that it had a slot on its rear that permitted a roll of plastic trace, fed into the machine by a clockwork mechanism, to make the dial operate realistically over the 24 or 48 hours of a weekend exercise.

The new polycarbonate cased meters were less delicate and this permitted them to be permanently stored at the monitoring posts instead of being retained at the group controls.