In my experience, most chains don't wear evenly. They usually develop "tight" spots that really aren't tight spots at all. Picking a section of chain and measuring it is not the whole story. You also need to spin the wheel and make sure that the chain play is constant along the whole length. What you will frequently find is that one section will have more play than the rest. If you adjust at the loose spot, you'll be too tight at the tight spot and vise versa. The proper way to check the chain is along the the entire length. I'm kind of tough on chains and replace them twice a season; as soon as I fine a loose spot, off it comes.