Answer: On analog scopes, multiple channels are displayed using either an alternate or chop mode. 

• Alternate mode : A display mode of operation in which the oscilloscope completes tracing one channel before beginning to trace another channel.

1. Alternate mode draws each channel alternately - the oscilloscope completes one sweep on channel 1, then one sweep on channel 2, a second sweep on channel 1, and so on.
2. Use this mode with medium- to high-speed signals, when the sec/div scale is set to 0.5 ms or faster.
3. In alternate mode an electronic switch alternates between signal A & B.

• Chop mode: A display mode of operation in which small time segments of each channel are traced sequentially so that more than one waveform can appear on the screen simultaneously.

1. This mode causes the oscilloscope to draw small parts of each signal by switching back and forth between them.
2. The switching rate is too fast for you to notice, so the waveform looks whole.
3. You typically use this mode with slow signals requiring sweep speeds of 1 ms per division or less.
4. In the chopped mode the switch free runs at very high frequency.