Optical Protractor (based on No9 Director)

[Tranter]

I’m trying to find out about another mystery I own item if anyone can help!  It’s a cased WW2 1943 dated Optical Protractor, made by Glass Developments Ltd (Ross) used as a bore sight for tanks or maybe SPG’s?  The optics are marked to the front lens retaining ring MG BORE SIGHT No 1008 DRG No 8680 next to the ROSS company logo.  The instrument is affixed to a heavy micro adjustable base with three machined steel feet to allow the instrument to be set up on the reference plate (flat) of a tanks main gun/machine gun or maybe even an SPG?  The base has a brass manufacturers plate stamped OPTICAL PROTRACTOR MADE BY GLASS DEVELOPMENTS LTD DRAWING No BA116-6C. The rotating  base comprises of the lower part of a director No9.  stamped  DIRECTOR No9 MK1 MSC 1943 No96. It’s all contained in its original wooden carry case with webbing strap. In good condition with clear optics and working adjustments etc.  An interesting instrument using No 9 Director components originally used for indirect fire use with the  Vickers machine Gun. It’s unclear whether this instrument was meant to be used on its base with the steel feet or whether the feet were in fact studs to locate into something horizontally which would then permit the user to look down through the eyepiece easily & more conveniently.  The only broad arrows are on the case hinges, there is no O.S. number or anything else that would indicate government ownership. 
I have never seen one of these before.  It’s interesting to see that it was a director No9, officially repurposed & modified to perform a different role.  Glass Developments were formed in 1938 becoming a limited company in 1944.  They were based in London (Brixton).  In 1994 the company was liquidated.  In their time they made all manner of items from glass buttons to optical instruments.