I just finished describing this technique to a client. It's similar to the Ruler Stretch in the way you can gauge tissue expansion in situ, but the difference is that the Ruler Squeeze is used to gauge girth while performing Squeezes. Using a cloth or plastic tape measure, wrap it around the central portion of your shaft that's left exposed when you do your squeezes, and secure it with a rubber band wrapped around the length of the tape. Be sure to have a little overlap so you can see where the beginning of the tape is in reference to the measurement. It's not "pretty" and you'll have to work at it to get an accurate reading, but once you get it down pat you'll be able to gauge just how much expansion you're putting your penis under.