Ok, I have to admit I'm challenged when it comes to getting things centered. I love this tool!!!!! It's the best thing around! One of the features I like about this type of ruler is that it takes the guess (calculation) work out of centering things that are a little off. It's easy to measure the center of a 6" peice of paper but when that piece of paper measures 5 1/3 " this makes it a little easier and much less time consuming.