You seem to be all confused in your head about standing waves.
You do not display standing waves on an oscilloscope, a standing wave is not a time-varying voltage.
The standing wave is a voltage which varies with the position along the line.
When you move the sliding carriage of the slotted line, with an ideal match (vswr = 1:1) the voltage will be the same at all points on the line. (OK so the voltage will vary at 10Ghz or whatever frequency, but the RMS value will be the same all the way along the line).
When the VSWR is 2:1, as you slide the carriage along the slotted line you will find that the voltage peaks and troughs, and the peak voltage is twice the trough voltage, because the VSWR is 2:1 !!
Note, whilst I have been refering to the VOLTAGE, if your slotted line is a co-ax, that is fine, but it is a bit of a streatch of the imagination to think of a voltage in a waveguide which is effectively a brass tube!
JimB