You will receive a nice Francis Barker & Son Combined Altitude Instrument & Prismatic Compass with case

In very good condition, "FB&S (1932) Ltd" is the stamp on the front of the compass (PATENT NO 1926 is on the dial) and was the type of instrument often used by civil engineers and also artillery regiments in the British army for range and trajectory calculations to target heavy guns.

A precision instrument in good working order, it weighs 14.9 oz in its leather case and measures 3" in diameter across the main body. 

It has a dual purpose function in that it incorporates a prismatic compass consisting of a green card dial with a 360 degree scale, and an Inches per Yard clinometer visible in the vertical plane.

These two functions are controlled by the brass button on the side which locks the compass when using the clinometer, and vice versa.

Please check pictures !!

Thanks for looking!!