I use that shelf liner stuff. I found a roll of it at the dollar store but Walmart and a lot of other places sell it also. Cut a strip and put it under your ruler - no need to glue it on - just move it when you move your ruler. Works like a charm. I also put a square of it under my foot pedal & I sit on a square of it as I have trouble sliding down in my chair. I've tried other things but this stuff works the best for me and you can't beat the price!!