DFM is a tool with a digital display for direct measurement of fuel consumption, which is used as a part of GPS tracking systems, vehicle telematics systems or as a stand-alone (autonomous) solution for fuel consumption monitoring. This solution is intended for small stationary units or small fleets operating within an enclosed area. The DFM-D differential fuel flow meter is designed for diesel fuel consumption measurement in fuel lines of vehicles and stationary engines. It is used as a part of the GPS vehicle tracking system. In addition, DFM-D registers the working time of the engine in various operation modes.