A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2014 Jun 17, 14:47 -0700
You need to be sure that the scales are being printed to their actual size with no scaling or that both are scaled by exactly the same amount. You can easily check that this is case in vertical direction. Just for reference the original vertical spacing between the successive cycles on the scales is 0.2 inches.
In the horizontal direction you can easyily check that the correct ratios are being maintained between lengths of cotangent and cosine scales. For example,
( log(cot(51°30')) - log(cot(45°)) ) / ( log(cos(71°30')) - log(cos(66°30')) ) = 1.0017
So referring to the file BygraveAltFlat.pdf in http://fer3.com/arc/m2.aspx/Postscript-code-for-making-Bygrave-Scales-Stuart-mar-2014-g27398 if you measure the horizontal distance between 45° to 51°30' on the the 20th row of the cotangent scale, it should be 1.0017 times longer than the distance from 66°30' and 71°30' on the 5th row of the cosine scale,