text: I learned to use one of these several years back and after leaving the organization where I had one to borrow, I had to get one for myself. Checking derailleur hanger alignment should be routine maintenance as they tend to get a little out of alignment due to getting banged around. Use is simple — put bike in stand, remove derailleur, attach alignment tool, check alignment, fix, remove, replace derailleur. Then go out and enjoy a bike which shifts like new again. Assuming you also maintained cables and shifters.