Hi there, I'm wondering if anyone has seen one of these before? It's about 11" across, designed to be panel mounted, made of aluminium I think. Obviously it's compass related, has a rotating circular grid under the perspex top. On the back it has the war department broad arrow and 'Stores Ref 6b/319'. In red letters with Variation west and Variation East so I'm guessing thats a magnetic variation correction. The weight saving cutouts on the back makes me think it could be aviation related, although it is a bit large for use on a plane itself, maybe it was training related. I'd say it's not as old as ww2, possibly 50's or 60's. The perspex is roughened, possibly for use with a china pencil. Any ideas anyone?