You observe the lower limb of the Sun at a sextant altitude (hs) of 54°28.2' on 22 July . The index error is 1.5' off the arc. The height of eye is 56 feet (17.1 meters). What is the observed altitude (Ho)?

54°30.9'

54°36.2'

54°37.7' ✓ Correct Answer

54°37.9'

USCG NMC Regulatory Explanation

Index error occurs when the sextant index mirror and horizon glass are not parallel at 0° 00.0'. 'On the arc' errors are subtracted; 'off the arc' errors are added to sextant altitude readings.

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You observe the lower limb of the Sun at a sextant altitude (hs) of 54&#176;28.2' on 22 July . The index error is 1.5' off the arc. The height of eye is 56 feet (17.1 meters). What is the observed altitude (Ho)?

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