If the sextant index error is OFF the arc, what correction is applied?

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Multiple Choice

If the sextant index error is OFF the arc, what correction is applied?

When the index error is off the arc, you must apply a correction to the observed altitude to account for the misalignment of the index with the arc. If the index error is off the arc toward you, the sextant reading is smaller than the true altitude, so you add the magnitude of the index error to the observed reading to obtain the true altitude. For example, a reading of 35°15' with an index error off the arc toward you of +0°05' becomes 35°20'. If the error were off the arc away from you, you would subtract it instead. So the correct correction here is to add the error (toward you).

When the index error is off the arc, you must apply a correction to the observed altitude to account for the misalignment of the index with the arc. If the index error is off the arc toward you, the sextant reading is smaller than the true altitude, so you add the magnitude of the index error to the observed reading to obtain the true altitude. For example, a reading of 35°15' with an index error off the arc toward you of +0°05' becomes 35°20'. If the error were off the arc away from you, you would subtract it instead. So the correct correction here is to add the error (toward you).

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