A clip-on ammeter includes a current measurement unit, an evaluation unit and a USB interface. The current measurement unit records current values and provides the current values as measurement values for transfer purposes. The evaluation unit includes an ND converter and is connected to the current measurement unit. The evaluation unit allows the measurement values to be transmitted in a processable form as USB compatible digital data to the USB interface. The USB interface is connected to the evaluation unit and the USB interface allows the USB compatible data to be made available for transfer purposes to be further processed. The evaluation unit is energized via the USB interface. The clip-on ammeter includes a voltage transformer. The voltage transformer provides a stabilized voltage as a reference voltage for the current measurement unit.