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The Elevation Reading on My Forerunner 645 Is Wrong
The elevation reading you see comes from a barometric altimeter sensor inside the watch. This sensor detects barometric pressure changes in order to determine current elevation at a given point. If you believe the elevation reading from your watch is incorrect, review the following information to help troubleshoot the problem.
Clean the Sensor Port on the Watch
A blocked or clogged sensor port can lead to issues such as:
IMPORTANT: Do not insert anything into openings on the watch. This can damage the internal sensor.
Weather Changes Can Affect Sensor Accuracy
Weather can contribute to an incorrect reading. This includes:
Incoming or Departing Low or High Pressure System
This can cause your starting elevation reading to be too high or low. You should manually calibrate to a known elevation in this case. The elevation gain/loss during the recorded activity is typically not affected.
A Windy Day
Wind can affect the sensor causing an inaccurate reading. If you are going to record an activity outdoors when it is windy we suggest wearing the sleeve of a shirt or coat over the watch.
Calibrate the Sensor
With proper calibration the watch can achieve an accuracy of +/-50 feet at any given point. Use the information below to determine which calibration options are best for you.
Manually Calibrate the Sensor
Make sure you are outside with a clear open view of the sky around you.
Press and hold the Up button to enter the Main Menu.
Press the down button 8 times and select Sensors & Accessories.
Select Altimeter.
Select Calibrate.
Select an option:
Enter current elevation? (Yes): Use this option to calibrate if you know the current elevation. This option offers the most accurate calibration.
Use GPS: This mode will determine your elevation through GPS triangulation. Elevation calibrated through GPS is accurate to +/-400 feet at any given point and is the least accurate.