Total correction

10.7.- TOTAL CORRECTION

10.7.1.- Definition

It is the angle formed by the north needle with true north. That is, it is equal to the algebraic sum of dm and deviation.

Ct = dm + Δ

10.7.2.- Calculation from declination and deviation

Once the magnetic declination (dm) is known, either from the chart or from the problem, and the deviation is known, either from the data provided by the problem or from having the deviation table, it is enough to add both data algebraically to know the calculation, so for example if the magnetic declination is 6o NW and the deviation when sailing on a given course is 3o NE, the value of the total correction will be:

Ct = dm + Δ = – 6 + (+ 3) = – 3o
It is important to keep in mind that the Total correction varies with each heading since although the dm remains constant the deviation will depend on the heading.