Celestial Navigation · Sextant Corrections
If the index error of a sextant is 'on the arc,' the correction is:
- AAdded to the sextant reading
- BDoubled and then added
- CSubtracted from the sextant reading✓ Correct
- DIgnored because it cancels out
Explanation
The rule is 'if it's on, it's off; if it's off, it's on.' Index error on the arc is subtracted; off the arc is added. Index error is found by setting the horizon in coincidence and reading the arc.
Authority: Bowditch (Pub. No. 9)
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