DUAL & CHOP  

In "Dual" mode (two-channel-mode) the signals from channels 1 and 2 are displayed on the screen at the same time. The real oscilloscope however only has a single electron beam. The beam alternately draws one waveform, then the other, on each sweep. To the observer this appears as if both waveforms are drawn at the same time. "Chop" mode can be used to display two signals on the screen at the same time.