SUUNTO Core - Manual (Page 24)

7.1.1 Getting correct readings
If you are engaged in an outdoor activity that requires you to know the air
pressure, you need to enter the altitude reference value for your location. This
is found on most topographic maps. Your Suunto Core will now give you the
correct readings.
To get the correct altitude readings, you need to enter the sea level air pressure
reference value. The sea level air pressure reference value relevant to your
location can be found in the weather section of the local newspaper or on the
websites of national weather services.
Absolute air pressure is measured constantly
Absolute air pressure + altitude reference = Sea level air pressure
Absolute air pressure + sea level air pressure reference = 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. If local weather is stable, you do not need to set reference values.
7.1.2 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.
24