Which navigational error increases when a marine sextant's horizon mirror has significant perpendicularity error relative to the frame?

💡 Explanation

When the horizon mirror is not perpendicular to the frame, ‘side error' introduces a larger angular displacement in observations, which scales inversely with observed altitude as the angle approaches the horizon; small angles will show proportionally large errors. Therefore bearing errors at lower altitudes will increase, rather than consistent latitudinal offsets, random longitudinal variations, or altered timekeeping.

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