VDO M4WL Operator's Manual page 45

M4 WL
Recalibrating the altitude before starting
In addition to choosing between the two start altitudes,
you can also enter a value under "current altitude".
Do this if you are not setting off from either start altitude 1 or
start altitude 2.
Press the SET button to select "Actual Alti".
The setting opens.
Set Set
Meter Feet
Press the BIKE button to increase the value.
Press the ALTI button to decrease the value.
Once this value has been set, confirm the setting
by pressing the SET button.
The confirmation message "Set OK" appears on the display.
The newly set value for the current altitude is now displayed.
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