HEAVY MACHINE GUN PIECE OF KIT

Wondering if anybody has any images or proof that this device was used by Heavy Machine gunners to ascertain the height of a distant house to lay fire down.
It is a fairly weighty item in immaculate condition with its leather pouch.
The gauge is wound up to lay the fine wire in the window on the building or hedgeline once the base plate has been levelled correctly.
It is fairly accurate, but wanted some proof of its use with heavy machine guns, as I have never heard of it being used.
Markings:
UIC makers mark MkVI Timbers 1940 Gun Sight With Broad Arrow & Leather Case Leather marked F.LTD MKVI

This is a field artillery piece not MG. There is a brilliant 1930s HMSO book on optics/accessories where this is featured for gun laying with a tripod.
Mark

Mark,
Could you put up the relevant page please. I was sure it had to be an artilleryman's piece. Imagine carrying that around in addition to all the MG spare parts wallets etc for a Vickers.;)