According to the text in VIDA, the instrument cluster oil level indication displays an average of the last three drive cycles. It will self correct without being reset, but because the indicated reading can be influenced by emptying and refilling the sump, especially if the car is also connected to VIDA and software updates or other service operations are being carried out which can cause the reading to deviate, the facility to software reset it exists to prevent spurious readings being presented to the customer immediately after a service until the system has had time to average its readings.
Yes, it is a stupid system, particularly as the oil level sensor itself sends accurate readings continuously. So designing the instrument indication to only work on readings averaged over a much longer period is dumbing things down to the extreme IMO.
At least for the VEA engine cars though, you can read the oil level directly from the sensor using the Torque android app with this custom PID:
Name "ShortName", "ModeAndPID", "Equation", "Min Value", "Max Value", "Units", "Header", "startDiagnostic", "stopDiagnostic", "Scale"
"Engine Oil Level", "Oil Level", "0x22da63", "float32(A:B:C
)", "0", "65", "mm", , , , "1"
VIDA says this regarding the sensor levels:
"The vehicle must be located on a level surface and with the engine off for a while so that the read-out value is reliable. The time depends on the current oil temperature as hot oil runs down into the trough quicker than cold oil. The longer the engine is off, the more reliable the value from the sensor is. If the oil temperature is below 80°C read off after 5 minutes minimum.
Hint: The 20 mm oil level (4.0 litres + 0.4 litres in the filter) corresponds to the parameter for low oil level (yellow information lamp) and 12 mm (3.7 litres + 0.4 litres in the filter) corresponds to the parameter for critically low oil level (red warning lamp).
The 51 mm oil level (5.4 litres + 0.4 litres in the filter) corresponds to the parameter for high oil level. The parameters apply at an oil temperature of 20°C."
My car (T2) had a 46mm oil level after its first service, and a 39mm oil level after its second service. Looking at the recommended service refill quantities for the VEA engines in the owners handbooks, the quantity keeps changing depending which model year handbook you read! It was originally 5.4 litres, then 5.9 litres and now stated as 5.2 litres. My Volvo dealer has been unable to explain why the recommended levels keep changing, but I intend doing my own oil changes from now on and will aim for 40-45 mm reading from the sensor after the filter has been refilled.