Indoors the initial calibration is based on the outdoor stride length. My stride is different indoors than on the TM and yes the calibrate feature can compensate for that. The problem there is my stride length changes with the TM pace causing mile auto laps to be early or late. I don't run the same pace every time. So I turned auto lap off and I manually hit lap at each treadmill mile. Garmin doesn't know it's a mile and it's pretty obvious that even if you calibrate at the end of the run, the laps use the previous calibration. The overall uses the new calibration for distance and overall pace.
It would be a bunch of software work to apply the new calibration to the existing data and probably not as easy to do as a person might think.
I'd personally like a manual 1 mile lap option for the treadmill. On a TM run if I hit the lap button it's a mile. Not the stop but\ton, just the lap button and leave the overall working just as it is. If I screw up pressing the lap button then the overall will still be correct after the calibration is done. But as long as I press the lap button at 1 mile intervals the data is going to be better than what I get now.
