I was doing a quick swap on a buddy's bike before a Saturday group ride in Austin and grabbed a 170mm crank arm off the shelf without checking. Turns out his old one was 172.5mm, and he felt the difference immediately on the first climb. I spent the next 20 minutes redoing it while everyone waited. How do you all keep crank arm sizes straight when you're in a hurry, do you color code or just double check every time?
Honestly, most folks can't tell 2.5mm without a tape measure, let alone on a climb. Sounds like that difference was in his head more than his legs, though waiting 20 minutes for a fix is the real pain.