Ch I/II & Trig I/II  

The button labeled "Ch I/II" (and "Trig I/II") is a channel selector button. "Ch" stands for "Channel." In single channel  mode the button determines which input signal is displayed on the screen. If the button is off, channel 1 will be displayed. If it is on, channel 2 will be shown.

In dual operating mode ("Dual", "Chop" or "Add" mode) the setting of the button determines which of the signals delivers the data for calculating the trigger timing. In this simulation both channels are triggered at the same time.