A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Roger Harris
Date: 2014 Jul 1, 20:38 -0700
The adjustable micrometer drum is common to C&P's higher-end sextants, viz. the "Bobby Schenk", "Polaris", and "Horizon Ultra".
It's curious that the sextant's owner did not know what this feature was, as it is described in C&P's catalogue and instructions for its use are of course included in the relevant "operations manual" (e.g., page 10 of the Horizon Ultra's manual).
If memory serves me correctly, the quick-adjust drum cannot be retrofitted on C&P's standard "Professional" model, which is equipped with a plain non-adjustable drum.