# Compass Error Calculation by Azimuth of Planets

Let’s learn how to calculate compass error by the Azimuth of any planet. We will understand this with the help of an easy example.

## Sample calculation (Azimuth- Planets):

On 06 May 2006 at 22h20m 10s UTC, a vessel in position 48°00’N 050°00’E observed Mars bearing 327° by compass. Find the compass error. If variation was 4.0° East, calculate the deviation.

GHA Mars (06d 22h): = 089° 55.7′
Increment (20m 10s): = 005° 02.5
v (0.9)             =     00.3
GHA Mars: = 094°58.5′

Longitude (E):  (+) 050° 00.0′ (plus-since longitude is easterly)
LHA Mars:                 144° 58.5

Declination (06d 22h): = N 024° 18.6
d (0.2): = 00.1 (D correction)
Declination Mars: = N 024° 18.5

Now we will FIND – P and use ABC method for further calculations.
P= 1440 58.5 (If LHA 180° P=LHA)
A = Tan Latitude/ Tan P
A = Tan 48° 00′ / Tan 144° 58.5
A = 1.584646985 N (A is named opposite to latitude, except when hour angle is between 090° and 270°).
B = Tan Declination/Sin P
B= Tan 024° 18.5′ / Sin 144° 58.5′
B = 0.787011353 N (B is always named same as declination)
C = A+B = 2.371658338 N (C correction, A+/- B: If A and B have same name-add, If different name- subtract).

Tan Azimuth = 1/(CX Cos Latitude)
Tan Azimuth = 0.6301399
Azimuth = N 32.2° W (Azimuth takes the combined name of C correction and Hour Angle – If LHA is between 0°and 180°, it is named “west”, if LHA is between 180° and 360, it is named “east).

True Azimuth= 327.8°
Compass Azimuth= 327.0°
Compass Error = 0.8° East
Variation = 4.0° East (you can find this in ECDIS when finding compass error onboard)
Deviation = 3.2° West

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