The monitoring of on-board fuel consumption metering (OBFCM) data is aimed at preventing a growing gap between the certified and real-world CO2 emissions from trucks. This can only be achieved, however, if regulation mandates a certain accuracy for the OBFCM methods in real-world operation. The first step in achieving this is to determine a reference method against which the on-road accuracy of the OBFCM methods will be validated.