Hi Bertil,
On
http://www.service.beetle24.de/, you will find the following explanation under "Longlife Service":
"By comparing the engine speed and oil temperature with the 'oil' characteristic curve stored in the engine control unit, a distance comparison value is calculated in meters."
So, if you actually drive 10 km with cold oil and high RPMs, for example, 40 km might be "deducted" to account for the increased wear and tear reflected in the maintenance records.
Similarly, the comparison of engine speed and engine load is made with the "soot" characteristic curve stored in the engine control unit. This results in a "soot load" value, which will also be included in the overall mileage calculation.
These two distance calculation values and the actual driving distance are continuously added separately as three variables within the engine control unit.
Now, the engine control unit calculates the remaining distance until the next scheduled service based on these three values and a time interval of 1 second.
You are taking good care of your engine when it is cold

.