If a magnetic compass is unaffected by any magnetic field other than Earth's, which statement is true?

The correct answer is that compass error and variation are equal when a magnetic compass is unaffected by any magnetic field other than Earth's.

In navigation, compass error occurs due to the difference between the magnetic direction indicated by the compass and the true direction (true north). Variation, also known as magnetic declination, is the angle between true north and magnetic north at a specific location. If the compass is solely influenced by the Earth's magnetic field and no other magnetic interference is present, the error it shows (due to variation) would directly correlate with the difference in angles between true north and magnetic north for that specific area. Thus, in such an ideal situation, you would find that compass error and variation are indeed equal.

In contrast, if compass north were true north, it would imply there is no variation at all, which is not typically the case in most locations. Geographic variations exist, and this choice does not hold under normal circumstances where the magnetic declination is present.

Similarly, if variation equaled deviation, it would suggest another form of error quantification that doesn't apply in this scenario, as deviation specifically refers to compass errors introduced by local magnetic fields or objects, which is irrelevant here since we are discussing an unaffected compass.

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