You can calibrate your product while your session is recording.

To do so, proceed as follows:

1. Starting from ALTI mode (altitude is shown on display), hold down the SETTINGS button (top right) for 3 seconds
   
   
2. The altitude will start to flash
   
   
3. Adjust to the altitude of your current location (obtained from a map or elevation marker) by pressing the buttons on the top right (+) or bottom right (-)
   
   
4. Once you've set the altitude, exit the menu by pressing the SETTINGS button (top left)