By default, altitude is measured with FusedAlti during exercises that use GPS and during navigation. When GPS is switched off, altitude is measured with the barometric sensor.
If you do not want to use FusedAlti in altitude measurement, you can disable it in the options menu.
To disable FusedAlti:
When the device is in time mode, you can search a new reference for barometric altitude with FusedAlti. This activates the GPS for a maximum of 15 minutes.
To search a new reference for barometric altitude with FusedAlti:
In good conditions it takes 4 – 12 minutes for FusedAlti to activate. During that time, Suunto Ambit3 Peak shows barometric altitude and ~ is shown with the altitude reading to indicate that the altitude may not be correct.