Tuesday, September 13, 2011
The Elegant Amplitude
The amplitude is perhaps the most elegant way to determine compass deviation and gyro error*. Use Bowditch table #27 (4 pages ) or a pocket calculator and the formula:
INV SIN [ SIN (Declination) / COS (Latitude)]
Apply the result to due East (90) or West (270) in the direction of the elevated pole when Latitude and Declination are of the same name (away if contrary). Take observations when the Sun's lower limb is 2/3 of a diameter above the visible horizon.
Tip- Keep a photo copy of Bowditch table #27 with the current years Nautical Almanac.
*Checking the compass/gyro at sea requires a celestial solution. Until the GPS compass becomes commercially affordable navigators will need to keep their celestial compass checking skills sharp.