I'm not sure what you are trying to do?
Here is an example of how to measure perfs.
http://www.youtube.com/watch?v=6-38SfQQZqQNow I'm not sure if you are working on the ( 2 Cents) or the (Two Cent) Washington. But the best way to start figuring out which you have is Perfs and Watermarks.
This is a fun stamp to spend some time on trying to figure out. But it can be full of turns and twists.