Typically calibration of AC value transducers are permanently calibrated due to the transformer based sensing topology. The circuit does not allow for drift during proper operation. It is our recommendation that the device be returned for calibration checkout. Please note that we will need to see if the device is still under warranty.
We would also recommend that you verify the waveform of your inputs is not affecting your readings. Any power measurement device will react differently to non-pure sinusoidal waveforms. Power meters typically have bandwidth specifications, and non-pure sinusoids contain harmonics and octaves other than the fundamental 60 Hz frequency, that cause variations in the output readings. Comparing two power meters together also must be carefully evaluated, as different power meters have different bandwidths and thus can give different readings. Our power transducers have a bandwidth of 4 Khz. Chopped waveforms, triangular waveforms, and other typical modern power systems will read significantly different than a pure sinusoid.
Please let us know how you would like to proceed.