On 16 January, you take a sight of a star. The sextant altitude (hs) is 4°33.0'. The temperature is -10°C, and the barometer reads 992 millibars. The height of eye is 42 feet. The index error is 1.9' off the arc. What is the observed altitude (Ho)?

Correct Answer: Option C — 4°17.0'

Applying index error (+1.9' off arc), height of eye correction from Nautical Almanac tables, and corrections for temperature and barometric pressure to the sextant altitude yields the exact observed altitude of 4°17.0'.