Celestial Navigation · Sextant — Index Error Determination
Index error is most commonly found by:
- AReading the chronometer
- BMeasuring the sun's altitude at noon
- CBringing the true and reflected horizon into one line and reading the displacement off zero✓ Correct
- DCounting the stars visible
Explanation
With the index set near zero, the direct and reflected views of the sea horizon are made to coincide in a straight line; the reading then shows the index error (on or off the arc). It can also be found on a star or the sun's limbs. The error is applied to every sight.
Authority: Bowditch (Pub. No. 9), The Marine Sextant
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