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