The 435A Power Meter and a compatible power sensor (sold separately) form a power measurement system. The system power level range, frequency response, and load impedance are dependent on the power system. The meter has a frequency range (dependent on power sensor) of 100kHz to 18GHz. The 435A meter is calibrated in watts and dBm. The accuracy is ?1% of full scale on all ranges. This accuracy is ensured by the following: an internal automatic zeroing circuit which removes error due to the ambient temperature output of the power sensing device, a calibration factor adjustment which accounts for error due to the frequency response of the power sensing device, and a internal calibration reference which has an output of 1 mW (?0.7%).