A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2014 Jun 27, 10:06 -0700
Over this last week I have had the chance to reduce various observations using an 8" circular slide rule. The 3 clockwise circular sine scales cover 60" and work well as cosine going counterclockwise. The multiplying scale is 25" and does close to 4 place calculations. Not as good as the cylinder rules but has the benefit of nesting nicely in the star finder pouch. The Doniol formula is reducing the best ( within 2.5' of calculator ) vs. the classic sine cosine ( within 5' of calculator ). Best results were obtained with 4 place tables and the circular rule for the single multiplication ( within 1' of calculator ). The down side is that the trig scales are degrees and tenths. The standard 10" rule is quicker for azimuth calculation where accuracy is not as critical. Attached is a reduction for the Sun this morning done entirely by circular slide rule for Hc. Red is done pre observation and black post observation. One thing for sure is that the circular slide rule is sailor proof (unbreakable).