A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John Brown
Date: 2014 Sep 9, 08:57 -0700
Looks like a Kelvin Hughes 'Mate' 3 Circle sextant. Very popular in UK merchant ships at one time, due to lowish cost. (About a month's pay, for a newly certificated 3rd Mate in the early 1960's).
Perhaps this is also the sextant on the front cover of Reed's Astro Nav tables.