Which error is magnified when a 18th-century navigators' sextant mirror axis isn't perfectly perpendicular to the instrument's plane?

💡 Explanation

When the sextant mirror axis isn't perpendicular, perpendicularity error introduces a cyclical error, because the measured angle varies as celestial bodies move across the sky systematically. The cyclical error results, rather than location specific date, biased speed, or specific latitude calculation which depend on unrelated navigational principles.

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