I have 3 different chain checkers. My eyes just aren't good enough for the ruler method anymore. The three I have are :
ProLink This one shows 100% wear on new chains. So it's useless
KMC digital. This one reads very little wear on worn out chains, Again useless.
Park CC-3.2 This one is the most accurate and my go to checker.
As someone mentioned above, check the chain in various places. I've noticed if you straddle the quick link with the checker, the chain shows more wear than other areas.