A test unit for testing inductive power charging of a mobile device, with a precisely calibrated power output, comprising an electrical circuit being powered by a DC power source, said circuit being capable of generating electrical power at each of a number of frequencies f, the electrical circuit comprising a primary transmitter coil for inductively transmitting power to a secondary receiver coil of the mobile device, and a capacitor connected in series with the primary transmitter coil in order to get a resonance circuit with resonance at a certain frequency, and a control unit configured to operate in a power calibration mode and a testing mode, wherein the control unit in the power calibration mode is configured to: receive a measurement of a voltage U supplied over the primary transmitter coil; receive a measurement of a current I flowing through the primary transmitter coil; and for at least one power frequency f of the number of frequencies: in a state where no secondary receiver coil is inductively connected to the primary transmitter coil: derive a time compensation parameter Δt(f) compensating for phase shift in the signal paths in the electrical circuit between the measured voltage U and the measured current I, such that the inductive power transmitted from the primary transmitter coil being a product of U and I integrated over a period equals zero by time compensating either of the measured U or measured I with the time compensation parameter, and store the time compensation parameter Δt(f) in a memory, receive from an external voltmeter a reference voltage measured directly over the primary transmitter coil for said at least one power frequency f and derive a voltage amplification constant K U-MDT (f) based on the reference voltage such that the voltage amplification constant K U-MDT (f) multiplied by the measured voltage U equals the reference voltage for said at least one power frequency f; and in a state where a secondary receiver coil of a calibrator unit is inductively connected to the primary transmitter coil: receive from the calibrator unit a calibration signal containing data comprising information of actual inductive power transmitted from the primary transmitter coil P TX-ACTUAL (f), and derive a current amplification constant K I-MDT (f) required for a calculated inductive power transmitted from the primary transmitter coil P TX (f) to be equal to that of the actual inductive power transmitted P TX-ACTUAL (f) for said at least one power frequency f, and store the current amplification constant K I-MDT (f) in a memory. a primary transmitter coil for inductively transmitting power to a secondary receiver coil of the mobile device, and a capacitor connected in series with the primary transmitter coil in order to get a resonance circuit with resonance at a certain frequency, and receive a measurement of a voltage U supplied over the primary transmitter coil; receive a measurement of a current I flowing through the primary transmitter coil; a voltage amplification constant K U-MDT (f) based on the reference voltage such that the voltage amplification constant K U-MDT (f) multiplied by the measured voltage U equals the reference voltage for said at least one power frequency f; and in a state where a secondary receiver coil of a calibrator unit is inductively connected to the primary transmitter coil: receive from the calibrator unit a calibration signal containing data comprising information of actual inductive power transmitted from the primary transmitter coil P TX-ACTUAL (f), and derive a current amplification constant K I-MDT (f) required for a calculated inductive power transmitted from the primary transmitter coil P TX (f) to be equal to that of the actual inductive power transmitted P TX-ACTUAL (f) for said at least one power frequency f, and store the current amplification constant K I-MDT (f) in a memory. receive from the calibrator unit a calibration signal containing data comprising information of actual inductive power transmitted from the primary transmitter coil P TX-ACTUAL (f), and derive a current amplification constant K I-MDT (f) required for a calculated inductive power transmitted from the primary transmitter coil P TX (f) to be equal to that of the actual inductive power transmitted P TX-ACTUAL (f) for said at least one power frequency f, and store the current amplification constant K I-MDT (f) in a memory.