A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2018 Mar 14, 11:10 -0700
The Clark nomogram that Roger attached here is again using graphical methods to multiply a pair of numbers. The equation uv = w is solved by setting f3 = 1, g3 = 0, g1 = u, g2 = -v and h3 = w in the notation of that document. Unlike the parabolic nomogram the middle scale is not linear in the product which further compresses the scale as declination increases and presumably explains why the diagram is only applied to the Sun.
The equation to be solved in this case is sin d = cos L sin A where A is the amplitude.
Plugging f3 = 1, g3 = 0, g1 = cos L, g2 = - sin A and h3 = sin d into the expressions for Scale 1, 2 & 3 with b = -a generates the nomogram.
Nomograms have been discussed previously on Navlist and a useful introduction can be found here.