What is this instrument for?

[Lang]

Bob,

It certainly is a clinometer which just means "angle measurer" but this particular variation is an Abney Level.

All artillery and mortars plus indirect machine guns have clinometers which are a much simpler version of the Abney Level. Before modern digital instruments they usually consisted of a simple brass arc with a level. You set the angle on the instrument then elevated the gun or mortar until the bubble was in the middle.

I am sure the artillery guys can put up a photo of a 25 pounder clino which is very similar to almost every weapon up to the digital era.

Lang