Suunto Ocean uses barometric pressure to measure altitude. To get accurate readings, you need to define an altitude reference point. This can be your current elevation if you know the exact value. Alternatively, you can use FusedAlti (see FusedAlti) to set your reference point automatically.
Set your reference point from the settings under Alti & baro.
When diving at altitudes greater than 300 m (980 ft), the altitude setting must be manually selected in order for the computer to calculate the correct decompression status. Failure to select the correct altitude setting or diving above the maximum altitude limit will result in erroneous dive and planning data.
See Altitude setting for altitude setting.
Suunto Ocean is not intended for use at altitudes greater than 3000 m (9800 ft).