Refers to the angle between Luobei and Magnetic North. This error is a systematic error when the compass is used in a small area, which is determined by the manufacturing error of the compass and the micro-magnetic field environment in a small area. When the compass is used in the field to determine the correct magnetic north direction, it is necessary to consider the correction of compass error.

The mathematical expression of compass error is: compass error = magnetic azimuth measured by compass-magnetic azimuth of the same target on topographic map.

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