Freestyle Nomad Manual page 9

NOTE: Altitude is measured by using an air pressure
sensor. Air pressure changes constantly due to varying
weather conditions. Therefore, measured altitudes in the
same position may vary. Pressure variations due to weather
conditions, or indoor air-conditioning, may affect altitude
readings. Calibrate the altimeter at regular intervals to
make sure it remains accurate.
NOTE: The pressure sensor range is: (-1600Ft) to (29,500Ft)
or (-500M) to (9,000M).
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