In most cases, the choice is one or the other. In some waveform monitors, the choice may be one plus the other, or one minus the other. It simply selects the input channel to be displayed. A third display choice is often the calibrate mode which displays an internal calibration signal. The internal calibration signal is usually a square wave and is 1 volt in amplitude.
Most waveform monitors have a selector or switch for scale voltage range.
This selects whether the vertical display is calibrated to show either 1 or 4 volts full scale. Most video applications require that the selector be set to 1 volt full scale display since video is specified to be 1 volt in amplitude. Sweep display or horizontal display selects the time period shown by the display. Standard choices are as slow as two fields of video per sweep to as fast as a small portion of one line of video per sweep. The choices are marked in various ways but most are similar to the TSM-60.