Which error amplified during multi-sight celestial navigation using an 18th-century sextant affects calculated longitude most significantly?

💡 Explanation

When index mirror parallelism is skewed, the resulting angular errors compound during successive observations because each measurement uses the same flawed reference, distorting derived celestial lines of position and calculated longitude. Therefore index mirror deviation predominately affects longitude, rather than perpendicularity, decentration, or filters which cause smaller or random inaccuracies.

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