What is this instrument for?

[Lang]

Terry is correct. I think I can make out the description on the side.

Could be used for all sorts of things but most useful to artillery shooting at distant high ground. They knew the horizontal distance from their position to the enemy feature by looking at the map. By using the Abney level they could get an angle and by a simple trig calculation find the exact height not just guessing off the contours. They then adjusted the gun range up to land at the right spot up the slope instead of at the bottom as would happen if they just shot the horizontal distance.

The Abney level was not as good as a theodolite but I should imagine the Forward Observation Officer would prefer to skulk in the bushes putting this up to his eye rather than stand up and erect a theodolite tripod!

They were very useful in the early days of railroad construction and the pioneering surveyors used them to mark out a realistic grade track through hilly country before going back to do it in detail with a theodolite.

Lang

[Bob Phillips]

Gentlemen: This device is also called a clinometer. I have a relatively new one which looks almost identical made by Keuffel & Ebber. If you google this info you will finds several articles/pictures.

[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

[Mike Cecil]

I agree with Lang, and the Clinometer Case in the background is the same as that which equipped both the 25pdr and 18pdr (all marks) from WW1 until the final withdrawal of the the 25pdr in the 1970s. It was carried on the inside face of the shield.

As I understand it, the hand clino was used to cross check the calibration of the inbuilt sight clino. Each time the sight was mounted (it was demounted and carried in a case when travelling), the hand clino was placed on the mark in the top of the breech block, and the two compared and the sight clino adjusted accordingly, to ensure the sight and barrel were in perfect 'cinque'.

Also used by the safety officer to check the angle of the barrel prior to a shoot in peacetime, and I believe a version is still in use for this purpose. The digital age is one thing, but physical checks are still required and carried out to ensure the rounds will impact where intended. A small deviation in angle at the gun will cause a round to impact short or long of the target by many meters. The danger of this is obvious.

Mike C