Abstract: A waveform storage and display system particularly useful in digital oscilloscopes is provided in which successive waveforms of a repetitive signal are compared with a reference waveform, and upon detection of a difference or change within the waveform, the changed waveform is automatically stored. In addition to the conventional acquisition and display waveform memories, a reference-waveform and a changed-waveform memories are provided. Once a reference waveform is selected and stored, comparison of subsequent successive waveforms to detect changes is achieved under microprocessor control. Several display modes to provide a visual indication of changes may be implemented.