On a wheel with 36 spokes, 0.006 of a revolution is about one fifth of a spoke interval.
When I said "marking your rim accurately and often" my "often" referred to the number of marks. I think you need more than 20 or 36 to be able to discern differences as small as 0.006 revolutions. But it's a small point because it's no big deal to measure out more marks on your rim.