Air Position Indicators

Following a recent house clearance we have acquired two heavy instruments in fair condition.

The instruments carry the following identification.

A M Ref No 6B/278
Air Position Indicator
Mk 1A

Serial No’s are 1117/43 & 1117/44

Can anyone please help with information regarding how, when and where these items were in use etc and if they are of any interest?

Frisby Historical Society.