NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2014 Mar 9, 12:25 -0700
Gary Lapook’s innovation of the Flat Bygrave uses a double copy of the cotangent scale so that you can always find the angle you are looking for without running off the edge. For reference I attach scales that are a close copy the ones Gary has produced and made available at https://sites.google.com/site/fredienoonan/other-flight-navigation-information/modern-bygrave-slide-rule
When it comes to Bygrave scales longer is better but doubling the cotangent scale doesn’t allow for optimal use of the available real estate on paper. I would therefore like to suggest an alternative configuration. When using a standard straight slide rule and the number you are seeking falls over the edge of the scale you move the slide by one scale length in the opposite direction. This operation has its analogue in the alternative Flat Bygrave attached here. The cotangent scale is no longer doubled and two pointers have been added to the cosine scale indicating the location of 0° and where 0° would lie if the scale were continued by one row down. Now if after lining up the 0° mark on the cosine scale the angle seeking falls off the scale, simply use the other pointer.
The scales in this alternative version are roughly twice as long as in the original and would allow for a inserting a greater number of tick marks for improved reading accuracy before the scales become too busy. In this version however I have kept the same number of tick marks and labels as the original.
Robin Stuart
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