The correct answer is A) deviation. Deviation is the horizontal angle between the magnetic meridian and the north-south line of the magnetic compass. This is caused by the influence of the ship's metal structure and equipment on the compass, which can cause it to point in a direction different from true north. The other options are incorrect: B) Compass error is the total error in the compass reading, which includes both deviation and variation. C) Dip is the angle between the horizontal and the direction of the Earth's magnetic field. D) Variation is the angle between true north and magnetic north, caused by the Earth's magnetic field.