Getting correct readings
If you are engaged in an outdoor activity that requires accurate sea level air pressure or altitude, you will first need to calibrate your Suunto Ambit2 by entering either your current altitude or the current sea level air pressure.
The altitude of your location can be found from most topographic maps or Google Earth. A sea level air pressure reference for your location can be found using the websites of national weather services.
Absolute air pressure is measured constantly
Absolute air pressure and known altitude reference = Sea level air pressure
Absolute air pressure and known sea level air pressure = Altitude
Changes in local weather conditions will affect altitude readings. If local weather changes often, it is advisable to reset the current altitude reference value frequently, preferably before starting your journey when the reference values are available. As long as the local weather stays stable, you do not need to set reference values.