How do I calibrate the altitude measurement?

In the App , in the “my watch” page, “calibration” menu, you can calibrate the altitude.

If the GPS of the phone is ON and gets a good altitude position, it will propose a value. Enter the actual altitude of your position to calibrate the watch altitude.

In the menu “general”, you can turn ON “auto altitude calibration”. The phone will regularly read the phone GPS altitude and send it to the watch as a calibration value."