A method for acquiring electrical signals from a living subject, including injecting, via an injection electrode attached to the subject, a known calibration signal to the subject and measuring respective levels of output signals generated at input electrodes attached to the subject in response to the calibration signal. The method further includes deriving respective weighting factors for the input electrodes in response to the respective levels, and applying the respective weighting factors to physiological signals acquired by the input electrodes, so as to generate respective corrected physiological signals.
