Help identifying Spitfire cockpit dial(?)

I am currently researching a crash of Spitfire (P8269) which crashed in a local field in May 1941. I have recovered a brass instrument, which I assume is a cockpit dial, but would like to know which dial it actually is..? The dial does not have a needle or face, only the internals survived. I have attached a couple of pictures, and there is a stamp on the back which says S&S 170, does anyone know what this could be...? Many thanks Centurian

 

Afraid I can't help directly, and having looked at the Pilot's Notes it's still difficult to be sure:

Supermarine Spitfire Mk II Pilot's Manual -- Read it online

But a couple of companies who maybe able to help you identify the part are:

Spitfire Aircraft Company, Ltd.
Spitfire Restoration - spitfire drawings for sale

Both restore Spifires and will have schematics

 

This schematic is easier to follow than the official ones:

 

I think its an altimeter.

To me the smaller knob is the one that would be used to adjust the altimeter due to pressure changes.

Looks like it's made of brass and is non electrical.

 

Did fighter pilots carry a pistol with them when flying, because ive found asmall round of ammunition on a spitfire crash site, length 35mm width 8mm

 

Hi Centurian, some pilots carried pistols, some didn't. While it was probably a part of the survival kit, I've noticed carrying a pistol seemed to be more prevalent in the Far East and Africa. That's based on my reading - I can't recall a UK-based example at the moment but that obviously doesn't mean it didn't happen.