How to Plot X/Y in Java Circuit Simulator
To create an X/Y plot in Falstad's Java Circuit Simulator, do the following:


Right click on the component that you would like to measure for your 'X' variable.
Select 'View in scope'.
Right click on the waveform and uncheck 'Show Voltage' or 'Show Current' to isolate the 'X' variable that you would like to plot.
Right click on the waveform again and select 'Plot X/Y'.
Place a scope probe where you would like to measure the voltage.
Right click on the waveform again and choose 'Select Y'.
Lastly, left click on the probe that you would like to use as your 'Y' axis.


Note that you can only measure voltages on the 'Y' axis of an X/Y plot!