You can improve accuracy of barometric altimeters by doing the following:
Make sure the unit has a calibrated barometer. You can do this by letting the unit sit at a fixed elevation for at least half an hour with a clear view of the sky to let the elevation trend to the correct number, or manually calibrating the barometer so that the elevation is correct.
Calibrating the Barometric Altimeter Your device was already calibrated at the factory, and the device uses automatic calibration by default.
You can manually calibrate the barometric altimeter if you know the correct elevation or the correct barometric pressure.
1 Go to a location where the elevation or barometric pressure is known.
2 Select Elevation Plot > > Calibrate Altimeter.
3 Follow the on-screen instructions
If weather is adversely affecting your altimeter (pressure is changing due to weather instead of elevation changes), you may disable it by setting the device to “fixed elevation” mode which will use GPS only for elevation data.
If you want to check the Total Ascent/Descent data fields set the track log record interval to once per second. This records all of the elevation data used to calculate the Ascent/Descent data fields in the track log which can then be used as a good reference.