A method of measuring the phase transient response of a device under test based on an instantaneous voltage waveform that represents an output signal of the device under test as it steps from a first frequency to a second frequency, the method comprising the steps of: calculating an instantaneous phase waveform based on the instantaneous voltage waveform; calculating an instantaneous frequency waveform based on the instantaneous voltage waveform; automatically estimating the second frequency, F2 EST, based on the instantaneous frequency waveform without any user intervention, wherein the automatically estimating step comprises the steps of: locating a segment of the instantaneous frequency waveform that corresponds to the period where the output signal has settled to the second frequency by identifying a set of contiguous points whose frequency values all equal the same frequency value within a specified tolerance range; and calculating the average frequency value of all of the points within the settled period to produce the estimate of the second frequency; and flattening the instantaneous phase waveform based on the estimate of the second frequency, wherein the step of flattening the instantaneous phase waveform comprises the steps of: generating an ideal instantaneous phase waveform comprising a straight line having a slope equal to 2π x F2 EST radians/second; and subtracting the ideal instantaneous phase waveform from the instantaneous phase waveform to produce the flattened instantaneous phase waveform. calculating an instantaneous phase waveform based on the instantaneous voltage waveform; calculating an instantaneous frequency waveform based on the instantaneous voltage waveform; automatically estimating the second frequency, F2 EST, based on the instantaneous frequency waveform without any user intervention, wherein the automatically estimating step comprises the steps of: locating a segment of the instantaneous frequency waveform that corresponds to the period where the output signal has settled to the second frequency by identifying a set of contiguous points whose frequency values all equal the same frequency value within a specified tolerance range; and calculating the average frequency value of all of the points within the settled period to produce the estimate of the second frequency; and locating a segment of the instantaneous frequency waveform that corresponds to the period where the output signal has settled to the second frequency by identifying a set of contiguous points whose frequency values all equal the same frequency value within a specified tolerance range; and calculating the average frequency value of all of the points within the settled period to produce the estimate of the second frequency; and flattening the instantaneous phase waveform based on the estimate of the second frequency, wherein the step of flattening the instantaneous phase waveform comprises the steps of: generating an ideal instantaneous phase waveform comprising a straight line having a slope equal to 2π x F2 EST radians/second; and subtracting the ideal instantaneous phase waveform from the instantaneous phase waveform to produce the flattened instantaneous phase waveform. generating an ideal instantaneous phase waveform comprising a straight line having a slope equal to 2π x F2 EST radians/second; and subtracting the ideal instantaneous phase waveform from the instantaneous phase waveform to produce the flattened instantaneous phase waveform.