A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2016 Jan 14, 20:09 -0800
I don't know why Bygrave used the same letter twice for his computation, "y" and "Y," (lower case "y" and upper case "Y," couldn't he buy a vowel?) quite confusing. That is why I use "W" in the place of "y" on my recreation.
The original Bygrave and MH-1 and 2 have the co-tan scale numbered from zero up to 90 and then back down to 180. In order to keep my scales uncluttered, I only include the scale in one direction, from zero up to 90 only, which then requires getting "Y," (I use the capital "Y" the same as Bygrave does) into the range of zero to 90 so I use an intermediate value, "X" on the way to determine "Y" when necessary. This is also a necessary step when using the Bygrave method on a standard slide rule. (This step is not needed on the original instruments or if using a calculator since the calculator can handle all the values, it gets the trig functions right.)
It is also then needed to get the hour angle (0 to 180 east and west) into the range of 0-90 only east and west, I call this angle "H" and my form shows you how to accomplish this.
My method deals with some special cases that neither Bygrave nor the Germans handled.
See my website: