No matter how calibrated the watch is, treadmill runs will never have the exact distance midway through a run.
I ran 5 miles on the treadmill, by the time the watch hit the 5k mark, my actual distance was a quarter mile off from the watch's estimate.
My 5k record was set to the time for that estimated distance, which was not accurate.
Only the final saved/calibrated distance of treadmill/non gps runs should be used for personal records, and only for the full distance of the run.
If I want my 5k time on a treadmill, I'll run 5k and enter my correct time after the workout is complete.
