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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:

  • Wrong elevation or barometer readings

  • Incorrect floors climbed credit

To find the barometric altimeter port please refer to:  The Floors Climbed Feature Is Not Accurate on My Watch

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.

  1. Press and hold the Up button to enter the Main Menu.

  2. Press the down button 8 times and select Sensors & Accessories.

  3. Select Altimeter.

  4. Select Calibrate.

  5. 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.