Celestial Navigation · Sextant Corrections — Index Error Off the Arc
An index error that is OFF the arc is applied to the sextant reading by:
- AAdding it✓ Correct
- BSubtracting it
- CIgnoring it below 3'
- DDoubling it first
Explanation
Index error off the arc is added to the sextant altitude; index error on the arc is subtracted. The mnemonic is 'if it's on, take it off; if it's off, put it on.'
Authority: Bowditch (Pub. No. 9), Sextant Errors
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