# NavList:

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

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Refraction:Which formula for Heights below 15°
From: Herman Dekker
Date: 2022 May 16, 13:26 -0700

Hello Navigators,

If the measured altitude (h) is <15° I learned in Franks  Advance Moderen Cel.Nav. Workshop:

I: R=1.0’/Tan [h+6.82/(h+4.024)]

In Henning Umland’s “A Short Guide to Cel.Nav.” the used formula is:

II: R=1.0’/Tan[h+7.31/(h+4.4)]

Can you explain the difference values?

If I calculated f.i. for h=0°,1°, 5° and 10° the calculated values are:

h=  0°      1°       5°     10°

I:  33.79’ 24.29’ 9.92’ 5.40’

II: 34.47’ 24.32’ 9.88’ 5.39’

The difference is negligible. but where come the different values in the formula from?

Regards.
HermanD

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