My apple watch was perfectly calculating the distance I travelled, but this week it has started to grossly underestimate my distance. I run on a treadmill - so I know the distance precisely. It used to work - now it doesnt. What happened?

Hi

The following steps may help:

Check that your personal information is accurate:

• On your iPhone, in the Watch app, go to: My Watch (tab) > Health > Edit - tap and adjust items, then tap on Done.

Calibrate your watch:

• Calibration can improve the accuracy of estimations made by Activity app and Workout app.
• You may wish to reset existing calibration data first.
• Instructions for each are available via the link below.

More information:

• Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
• Use the Activity app on your Apple Watch - Apple Support
• Use the Workout app on your Apple Watch - Apple Support