A test and measurement instrument having a signal generator circuit and a waveform monitor circuit for monitoring a waveform received at a device under test (DUT). The signal generator circuit generates a waveform based on an input from a user, while the waveform monitor circuit sends captured signals to a processor to determine a waveform received at the DUT. The waveform monitor captures a signal at a first test point and a second test point, via a switch, and the processor receives the captured signals and using linear equations determines both an incident waveform and a reflected waveformfrom the DUT.