This invention relates to a system for making a record of the amount of work actually produced by an arc welder or similar machine for a given period of time. The arc welder may be energized, for example, for eight hours but may be actually welding for only four or five hours. The system includes a current sensor which records only when at least minimum arc currents flow, and a voltage sensor which records only when at least voltages sufficient to sustain an arc and which are greater than those at which short circuit occur. The simultaneous occurrence of both such currents and voltages is necessary for recording.