# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Hc by Azimuth Diagram - finally
From: Hanno Ix
Date: 2013 Aug 2, 20:16 -0700
Greg:

you will remember I claimed hc can be found using the Azimuth Diagram I proposed.
In your response you suggested such a method might be helpful for setting the
sextant before making sights. At that time I promised a more detailed description. Here is now a sketch that indicates the method. I wished I could have presented this earlier but
a near catastrophic computer crash prevented it. I hope the sketch is easily enough to follow - just proceed from "1" to "5". For clarity I am using a color for each step.

I dont think there is a new form necessary if one wishes to use this method. Just convert mentally the scales left/top to sin and right/bottom to cos as indicated. The extension to angles from 90 to 180 will be made by applying the well known rules for this. Remember that sin(x) * sin(y)  = const. and cos(x) * cos(y) = const. are indicated by curves each of which stands for a particular value of the product which in turn can be read on the C-scale. Having found these products one enters them in the formula for sin(hc). The last step is finding the asin which is accomplished by drawing a straight line (step "5").

As often, the scheme easier to do than to describe. I hope it will be found helpful.

h

________________________

PS:   I also promised to describe a method with which one can perform sight reduction
by hand quickly. It uses only 4 digit integers, needs no logarithms, and uses just additions, subractions and simple multiplications by 2 and 4 . The tools neccessary are pencil, paper and a 2 page cos-table. Now that my computer has been resuscitated somewhat I am working on finishing a detailed description, the worksheet and the cos-table. I hope to be done soon.

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