On 31 October your 1700 zone time DR position is LAT 27°17.0'N, LONG 116°10.0'W, when an amplitude of the Sun is observed. The Sun's center is on the visible horizon and bears 246.5° per standard magnetic compass. Variation in the area is 8.5°E. The chronometer reads 01h 01m 23s and the chronometer error is 01m 54s slow. What is the deviation of the standard compass?

Question

On 31 October your 1700 zone time DR position is LAT 27&deg;17.0'N, LONG 116&deg;10.0'W, when an amplitude of the Sun is observed. The Sun's center is on the visible horizon and bears 246.5&deg; per standard magnetic compass. Variation in the area is 8.5&deg;E. The chronometer reads 01h 01m 23s and the chronometer error is 01m 54s slow. What is the deviation of the standard compass?

Accepted Answer

Option B: 0.8&deg;W. Calculate the Sun's declination for the observation date. Use the amplitude formula sin(Amp) = sin(Dec) / cos(Lat) to find the true amplitude. Convert this to a true bearing. By applying the 8.5°E variation to the compass bearing, the difference between true and magnetic headings confirms a deviation of 0.8°W.