64 seamanship secrets
Hold the micrometer drum and spin it one way or the other to perfectly align three things
at once: the index-arm mark, the zero-degree mark on the arc, and the zero-minutes mark
on the micrometer drum.
Turn the micrometer drum away from you about a quarter turn. You’ll notice the minutes
increase. When adjusting or checking for error, this is called on the arc. Subtract the
minutes to correct an observation.