Yes, that's it exactly. If you're six feet tall the 8 should be 24', if blades were exactly 12 inches it would be 12 foot circles. So 12 steps on each circle. So, make center snick mark, walk 12 one way, make a mark. Walk 12 the other way, make a mark. Then also do a crossways 12 on each circle. You end up with marks at 3/6/9/12 of the circle. It's a very rough way of laying a patch and was excellent for patch rotations where you got the end spot to see if you could fit or would have to overlap the person beside you.