SUUNTO AMBIT - Manual (Page 50)

9.1.1 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 Ambit 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.
9.1.2 Getting incorrect readings
ALTIMETER profile + standing still + weather change
If your Altimeter profile is on for an extended period of time with the device
in a fixed location while the local weather changes, the device will give incorrect
altitude readings.
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