On 25 December you observe the Sun's lower limb. The sextant altitude (hs) is 4°06.9'. The height of eye is 47 feet and the index error is 1.6' on the arc. The temperature is 19°F and the barometer reads 1030.8 millibars. What is the observed altitude (Ho)?

Correct Answer: Option B — 4°01.9'

Per Bowditch, apply index error (1.6' on the arc, so subtracted) to hs, then apply dip correction for 47 feet height of eye. Use temperature and barometric pressure tables to determine total refraction correction. Finally, add semi-diameter for the lower limb to yield the observed altitude (Ho) of 4°01.9'.