priming the oil pump

Newbomb Turk said
20 degrees is .4028 inches. So .400 thou would be plenty close enough.

I took the dampener diameter (7.25") times Pi (3.1416) = 22.7766" circumference. divide that by 360 gives 0.0632683" for each degree & times 20 degrees would be 1.625" around the dampener. Am I wrong on this?