With the azimuth mirror on the compass the direction of a celestial body can be determined, expressed in degrees. Used, among other things, to determine the deviation of the compass.
The black lackered, brass instrument comes with a loose pen in a mahogany case with leather carrying strap.

Catalog: NM.5-47
Date: ca. 1940
HWL: 13x22x24 cm
HWL case: 16x26x25 cm
Signed: Kelvin, Bottomley & Baird Ltd. Glasgow
Origin: England
Condition: in perfect condition, wear consistent with age and use