🔍 Key Concepts

• Index error (off the arc vs. on the arc) and how it changes the sextant altitude • Dip correction for height of eye and that it is always subtractive from hs for sights taken from above sea level • Semi-diameter and lower limb corrections taken from the Nautical Almanac for the Sun

💭 Think About

• Start by deciding whether you add or subtract the 2.0' index error when it is "off the arc" and apply that to hs to get the apparent altitude (Ha). • Convert the height of eye from feet to meters (or vice versa) and think about how dip is found and applied—does it make the apparent altitude larger or smaller? • Remember that for the lower limb of the Sun, you apply a correction from the Nautical Almanac; consider whether that correction generally increases or decreases the altitude for normal daytime sights.

✅ Before You Answer

• Be sure you understand whether "off the arc" index error is numerically positive or negative and how that affects the correction sign. • Confirm that dip is always a negative correction (you subtract it) when you are above sea level. • After applying all corrections step by step (index error, dip, then Sun’s lower limb correction), check that the final Ho is close to but not equal to the original hs and that your total correction is within a few arcminutes, not tens of minutes.