Apparatus for calibrating a transmitter of a first integrated circuit, the transmitter being capable of transmitting a signal at N different transmit power levels based on N respective calibration values stored in the first integrated circuit, wherein N>1, the apparatus having corresponding methods, comprise: a power meter to measure a received power level of the signal transmitted at one of the N power levels; and a calibration circuit comprising an adjustment circuit to adjust the calibration value for the power level until the received power level of the signal falls within a predetermined range, and an offset circuit to replace each of the calibration values for the N−1 remaining transmit power levels based on the adjusted calibration value for the transmit power level and a respective predetermined offset from the adjusted calibration value.