On 4 July you observe the lower limb of the Sun at a sextant altitude (hs) of 25°29.8'. The index error is 3.1' off the arc. The height of eye is 48 feet (14.6 meters). What is the observed altitude (Ho)?

25°37.1'

25°40.2' ✓ Correct Answer

25°42.8'

25°44.3'

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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On 4 July you observe the lower limb of the Sun at a sextant altitude (hs) of 25&#176;29.8'. The index error is 3.1' off the arc. The height of eye is 48 feet (14.6 meters). What is the observed altitude (Ho)?

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