Elevation Auto Calibration

Hi everyone.

Everytime I start to record an activity on my Edge 830 I get this message "Elevation calibrated to location" and immediately the elevation number goes up by +/-12m out of the blue with me standing still in the same spot.

The problem is that the elevation shown right before I press the record button (before the "auto-calibration) is more accurate than the one modified. 

How do I turn off this feature?

Thank you.