A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2021 Feb 27, 14:35 -0800
It is not ncessary to make or have made special prisms with silvered faces, as they already exist in sets of angle gauges. These are blocks of steel with highly polished faces at angles accurate to better than 3 seconds. They can be wrung together to add angles and if swung through 180 degrees the angles subtract. The 18 and 30 degree ones shown can add to 48 degrees or subtract to 12 degrees. My extensive set from the former Soviet Union can set up angles from 1 minute to 360 degrees, but with a set of only thirteen blocks it is possible to set up any angle though with less convenience, as several blocks may have to be used.The angles are 1, 3 ,9 ,27, 41 and 90 degrees with 1, 3, 9, and 27 minutes and 0.1, 0.3 and 0.5 minutes. As an example, 8 deg 14 min could use 9 deg - 1 deg + 27 min - 9 min - 3 min - 1 min. Typically, the faces are about 90 x 15 mm.
I have no plans to use them to calibrate my sextants...