Celestial Navigation · Sextant — Adjustable Errors
Which sextant error is an ADJUSTABLE (correctable by the navigator) error?
- AGraduation error of the arc
- BPrismatic error of the shades
- CIndex error (and perpendicularity/side error)✓ Correct
- DCentering error
Explanation
Perpendicularity, side error, and index error are adjustable by the mirrors' set screws; index error that remains is measured and applied as a correction. Non-adjustable (instrument) errors — graduation, centering, and prismatic/shade errors — are determined once and treated as a fixed instrument correction.
Authority: Bowditch (Pub. No. 9), The Marine Sextant
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