Question 1

On a micrometer sextant you read…

Accepted Answer

Whole degrees from the arc, minutes and tenths from the drum — Arc = coarse, drum = fine; one full drum turn is one degree of arc. 40° on the arc and 32.5 on the drum is 40°32.5′.

Question 2

The index mark sits just LEFT of the arc’s zero. The drum shows 57.0. The reading is…

Accepted Answer

3.0′ OFF the arc — read the drum backwards from 60 — Off the arc, the drum counts down from 60: 60 − 57 = 3′. Off-the-arc index error is ADDED to sights (“off the arc, put it on”).

Reading the arc and the drum

This lesson is part of a paid course