Gyro Error Calculation

Find the gyro error if the setting sun was observed to bear 290° PGC at Lat 37° 10' S. Declination 13° 37' N.

Given:

     Latitude = 37° 10' S
Declination = 13° 37' N

What is asked?

Gyro error

Solution:

                Sin amplitude = Sin Declination
                                         Cos Latitude
                                     = Sin 13° 37' 
                                        Cos 37° 10'
                                     = 0.23542
                                        0.79689
                Sin Amplitude = 0.29542
                                     = 0.29542 inv Sin 
                      Amplitude = W 17.18° N          (West because the sun is setting)
                                          +    270°             (plus 270° because it is in the 4th quadrant)
                  True azimuth = 287.18°
                        per Gyro = 290°               (subtract to get gyro error)
                      Gyro Error = 2.8° W         (Compass best, error west; compass least, error east)

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