On 2 January your vessel's 1948 zone time position is LAT 21°42'S, LONG 39°12'W, when an amplitude of the Sun is observed. The Sun's center is on the celestial horizon and bears 260° per standard magnetic compass. Variation in the area is 19°W. The chronometer reads 10h 44m 36s and is 03m 24s slow. What is the deviation of the standard magnetic compass?

Question

On 2 January your vessel's 1948 zone time position is LAT 21&deg;42'S, LONG 39&deg;12'W, when an amplitude of the Sun is observed. The Sun's center is on the celestial horizon and bears 260&deg; per standard magnetic compass. Variation in the area is 19&deg;W. The chronometer reads 10h 44m 36s and is 03m 24s slow. What is the deviation of the standard magnetic compass?

Accepted Answer

Option A: 4.3&deg;E. Convert zone time to GMT to find the Sun's declination. Calculate the True amplitude using the standard formula sin(Amp) = sin(Dec) / cos(Lat). The resulting True bearing compared against the compass bearing gives the compass error. Applying the 19°W variation to the compass error results in a deviation of 4.3°E.