You observe the lower limb of the Sun at a sextant altitude (hs) of 46°20.3' on 1 April. The index error is 4.5' off the arc. The height of eye is 57 feet (17.4 meters). What is the observed altitude (Ho)?

Correct Answer: Option D — 46°32.6'

Apply the index error of 4.5' (off the arc is additive) to the sextant altitude. Subtract the dip correction for a 57-foot height of eye. Finally, apply the semi-diameter and refraction corrections from the Nautical Almanac to arrive at the correct observed altitude (Ho) of 46°32.6'.