Free field strength meter, type EP 594 FM. Quite a nice device, not sure how much use it is now with digital transmissions, although still useful for FM transmissions I suppose. In the analogue tv days, you could check for the strongest signal by tuning to a station - you could hear the sound of the station and adjusting the aerial to get the maximum signal strength.

Would have taken batteries or an external power source, but, the battery holder is now missing (probably it leaked some time in the long past). I did have it powered the side connector, but I can't remember what voltage it took.

Must pick up from Churton Park, Wellington.