In the developed measuring tools measuring methods were implemented for informative parameters of harmonic signals using the discrete Fourier transform (DFT) and correction of measuring errors forphase difference and amplitude. Designed layouts based on the virtual instruments to the measuring instruments demonstrate the advantages of the method DFT, allow us to determine the specified metrological characteristics and to correct the errors of their measurement.As a comparing result values of error for estimate value of the phase difference without correction and error estimation of the phase difference with correction we clarified, that the corrective edits in designed phasemeter reduce more than factor 10 the level of error values of the measurement result of the phase difference in comparison with the results without applying a correction.The estimation error of the phase difference with correction has a back-quadratic dependence with the number of analyzed periods of the signal, which sharply decreases already when you change the number of periods from one to four.The accuracy of the calibrator phase shifts is determined by the instrumental error of the DAC and methodical error of creating signal and depends on the number of samples per signal period.The filters affect to error of the calibrator phase shifts can be minimized by ensuring the identity of their phase-and-frequency characteristics.Using more perfect methods of analog-to-digital conversion will improve performance, expand the bandwidth of the signals and increase the ratio signal/noise. Note that errors were made on the stage of analog-to-digital conversion, are difficult to separate from the converted signal and completely eliminate them during further digital processing. Therefore, you should pay attention to the value of the instrumental errors of the ADC and DAC.