**Sample calculation (Azimuth-Stars):**

Let’s LEARN WITH AN EXAMPLE –

*On 05 May 2006 at 11h00m00s UTC, a vessel in position 04°30’N 010°00’W observed Canopus – bearing 145° by compass. Find the compass error. If variation was 4.0° East, calculate the deviation.*

** GHA Aries ** (05d 11h): 028° 10.7° ** Increment** (00m 00s): 000° 00.0

(adding +)** GHA Aries:** 028° 10.7

**Longitude (W): ** – 010° 00.0′ (minus- since longitude is westerly)** LHA Aries: ** 018° 10.7

SHA Canopus: 263° 59.0

LHA Canopus: 282° 09.7′** **

**Declination:** S 052° 42.1

**P**= 360 – 282° 09.7° = 77° 50.3″ (IF LHA>180, P=360-LHA)

**A**= Tan Latitude/ Tan P

**A**= Tan 04° 30′ / Tan 77° 50.3

**A**= 0.016960803 S (A is named opposite to latitude, except when hour angle is between 090° and 270°)

**B** = Tan Declination / Sin P** B**= Tan 052° 42.1′ / Sin 77° 50.3** B **= 1.342905601 S (B is always named same as declination)

** C = A+B** = 1.359866404 S (C correction, A+/- B: If A and B have same name- add, If different name subtract)

** Tan Azimuth = 1/(C X Cos Latitude)** Tan Azimuth = 0.737640253

Azimuth = S 36.4° E (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= 143.6°

Compass Azimuth= 145.0°

Compass Error = 1.4° West

Variation = 4.0° East

Deviation = 5.4° West