A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Paul Brewer
Date: 2015 Oct 10, 15:44 -0700
I think it is actually a Gyro sextant. Used by the Kriegsmarine. The instructions have the mark of the German Coastguard bottom right.
I have one which I believe was part of a batch of instruments and machinery conviscated by the British at Wars end. Later sold off by the government as surplus.