During product development, the frequency spectra of disturbances needs to be measured frequently and compared against the limits set in current product standards. One newer method of measurement is a time domain scan which allows significant reduction in measurement times without affecting accuracy. This white paper uses the CISPR 16-1-1 compliant R&S ESR EMI test receiver as an example for making comparisons between the measurement speed and level measurement accuracy of a conventional stepped frequency scan versus an advanced FFT-based time domain scan.