Checking the magnetic compass at sea is a snap with the assistance of a pocket calculator and the azimuth formula
SIN azimuth = (COS declination x SIN meridian angle) / COS altitude
For the formula altitude use an estimated (hs) sun altitude by counting the solar diameters above the horizon and multiplying by 0.5 degrees. (hs) Altitudes above 3 degrees will require a sextant. Declination is easily retrieved from the Nautical Almanac. Meridian angle will require GHA from the Nautical Almanac and a DR longitude. Time should be to the second as per short wave time tick on frequency 5000, 10000, 15000, and 20000 kilohertz. Double check calculations with Pub. 249 tables.
The pictured calculator is a CANON F-710 which is an excellent value calculator for trig applications. Also recommended is a book CALCULATOR AFLOAT by H. H. Shufeldt
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