Question 646Navigation General

The correct answer is C) combined variation and deviation. Compass error is the combined effect of variation (the angle between true north and magnetic north) and deviation (the angle between magnetic north and the compass north due to the influence of the ship's magnetic fields). The total compass error is the combination of these two factors, which is why the correct answer is the combined variation and deviation. The other options are incorrect because: A) is only the difference between true and magnetic heading, not the full compass error. B) is incorrect because variation plus compass course does not account for deviation. D) is incorrect because deviation minus variation does not capture the full compass error.