# NavList:

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

**Re: Nomogram for Dip Short of Horizon**

**From:**Robin Stuart

**Date:**2018 Mar 19, 07:18 -0700

Herman,

I had anticipated your request and attach the nomograms with the “Height of Eye” metres.

Tony,

The nomogram is a representation of the equation

D_{s}=0.56578 h_{f} / d_{s} + 0.4158 d_{s}

rewritten as quadratic equation in d_{s }which does incorporate the effect of refraction. If you ignore it, the constants will change but you still get a quadratic. Thus the bend cannot attributed to refraction but is rather dictated by the form of the equation being solved, see for example http://lalashan.mcmaster.ca/theobio/math/index.php/Nomogram . Although I could have cut the “Distance to Waterline” scale off sooner I extended it unlabelled to 12NM for no really good reason.

The difference between the two nomograms is simply the length of the scales. In order to reduce their size I applied a shear that turns the “Distance to Waterline” scale from something that runs roughly horizontally to a diagonal. If you use DipShortNomogram5.pdf for say “Height of Eye” 5ft and “Distance to Waterline” of 1.5NM, such as you might get for someone standing on the water’s edge, you intersect the “Distance to Waterline” scale at a fairly shallow angle which I thought would be inconvenient and possibly introduce errors. If you are never going to be more than 25ft above the water then DipShortNomogram4.pdf is a better choice.

Regards,

Robin Stuart