The barometric altimeter on Outdoor watches use barometric pressure to determine changes in elevation, as well as changes to the pressure caused by weather patterns. Outdoor watches will continually monitor barometric pressure to determine which mode is most appropriate at any given time.

Auto (default setting) - The watch will monitor changes and automatically switch between altimeter or barometer modes
Altimeter - The watch is locked in altimeter mode and all changes in pressure will impact the elevation reading. This mode is best for activities with a lot of elevation changes.
Barometer - The watch is locked in barometer mode and all changes in pressure will be considered due to weather and changes in ambient pressure. This mode is best used for activities without a lot of elevation changes.

Factors that Impact Barometric Altimeter Measurements

Rapid changes in weather
- The watch will resume accurate altimeter readings when weather conditions settle.
- If experiencing rapidly changing weather, consider calibrating the sensor after conditions have settled.
Extended periods of time in a fixed location
- For best accuracy, +/- 50 ft (~15 m), calibrate the pressure sensor to a known elevation on regular basis.
Moving to and from climate controlled or pressurized environments (indoors to outdoors)
- Consider calibrating the sensor while you are outdoors.
Debris blocking sensor port
- Fluctuating barometer data or lower/higher than expected altitude may be caused by water, or debris in the sensor port (located between the Start/Stop and Back/Lap buttons).
- Clean the sensor port. See Related troubleshooting articles below for instructions.
Clothing covering the sensor port
- Fluctuating barometer data or lower/higher than expected altitude may be caused by articles of clothing covering the sensor port.
- Make sure the sensor port is not covered.

For information on manually calibrating your altimeter, see your Garmin Owner's Manual.