I haven't tried it on my rulers, but I just bought some to try on a piece of quilt I'm working on. It's a QAYG, and it's a long strip for the side of the quilt. I found that as I sewed, the strips I was sewing on were slowly but definitely getting lower and lower on the piece of backing. Then when I looked at it from a distance, I also realized they were no longer straight! I'm going to try using the painters tape to mark where the edge of the top would be. Did any of that make sense? In my brain, I know what I'm doing, but not sure that transfered to the written word.... oh well...brilliant idea, regardless! :D