Celestial Navigation · Sextant — Perpendicularity Error
Perpendicularity error of a sextant is checked by:
- AMeasuring the dip
- BReading the altitude of Polaris
- CTiming the chronometer
- DLooking into the index mirror to see whether the arc and its reflection form a straight line✓ Correct
Explanation
To check perpendicularity, set a moderate angle and look obliquely into the index mirror: the actual arc and its reflection should appear as one continuous line. A break indicates the index mirror is not perpendicular to the frame, and it is adjusted by its screw.
Authority: Bowditch (Pub. No. 9), Sextant Adjustments
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