Methods and apparatuses to perform calibration of imprecise sensors for power monitoring in a data-processing system are described. The system includes a load coupled to one or more sensors. An electronic load changes a first input signal through one or more sensors by a predetermined amount. A difference in an output signal from the one or more sensors in response to the changing is obtained. The output signal is measured and sampled. A distribution of samples of the output signal is determined. The estimated parameters of the distribution that most likely to explain actual data are determined. Next, a transfer function of the one or more sensors is determined based on the estimated parameters. The input signal through the load is accurately predicted using the transfer function of the one or more sensors to monitor the power usage by the load.