1. Coefficient C Pc due to force Q
By horizontal athwartship component of ship’s permanent magnetic field at compass position
Induced C due to f (vertical soft iron rod)rod induction at the compass position to port or starboard of the compass position. Normally not present on merchant vessels
Algebraic Sum
Total coefficient C

2. Coefficient C
Vessel’s deviation varies with cosine of the compass course
Maximum deviation on N & S headings
Zero deviation on E & W headings
+C if Easterly deviations on Northerly headings if Westerly deviations on Southerly headings
-C if Westerly deviations on Northerly headings if Easterly deviations on Southerly headings
Semi circular deviation

3. Coefficient C
Cause of coefficient C
Due to athwartship magnetic field at compass position
The above field may be due to 1) Force Q of ship’s permanent magnetic field 2) Induced magnetism on soft iron if the compass is poorly sited
+C if the field is directed to starboard side
-C if the field is directed to port side

4. Coefficient C
Effect of magnetic latitude
Smaller deviation in lower latitudes
Larger deviations in higher latitudes
Correction of Cp
By placing permanent magnets below the compass
in athwartship direction to counter act force Q

5. Coefficient C
Induced C ( Ci) This is due to induction in vertical soft iron whose effective poles are level with the compass card in athwartship direction (f rod). Normally on merchant vessel as the compass is carefully sited about F/A centre line vertical soft irons are equally disposed to port & starboard and induced C is NIL Correction not normally required if the compass is carefully sited Correction of Ci if the compass is off set from F & A centre line

6. Coefficient C induced

7. Coefficient C

8. Coefficient C
Total coefficient C Is the combination of Cp and Ci. In a particular locality Cp and Ci are inseparable. Combined effect of Cp and Ci causes maximum deviation on N/S headings and zero deviation on E/W Headings. Directive force Gain on DF on certain headings are exactly balanced by the loss of DF on other headings. So that the components which cause coefficient C have no effect on mean DF averaged over all headings at the compass position

9. Coefficient C

10. Coefficient C