Pete made the comment I was going to make - the calibration constant, or the clicks-per-mile(km) should have been a red flag! I know how many clicks I normally have in both my 1000-foot calibration, and for an entire mile. If they vary by more than a few clicks, I examine what I am doing.
I just discovered my Jones is broken when I did a calibration a few days ago. Normally have 3500 clicks, or so, in my calibration. but I had 4717, 4637, 4718, and 4677 clicks. Very easy to see that I had an issue.
Measurers need to pay attention to the clicks in the calibrations, as that is our first opportunity to recognize an issue (other than a flat tire when we begin a calibration!).