Tachographs are used to register vehicle travel information (instant velocity, mean velocity, distance travelled and travel time). As a fundamental device, its verification is essential for keeping the vehicle regularized. For certifying that vehicle and tachograph are properly calibrated, the Inmetro sets a two year inspection interval. The quantity of pulses that the velocity sensor sends to the tachograph, in the distance of 1000 meters, is hold in a constant K, and is used to keep the synchrony between the vehicle and the device. Currently, a 20 meter track method is used to obtain the constant K. This work proposes a new methodology to obtain the constant K using the global positioning system (GPS) as a reference for the distance with the purpose of designing a calibration process with the vehicle running on the road.