You can have the datapoints being plotted as points, or as lines. If you have downsampled the data 1:100, you may be better off with lines.

Drawing points is a bit faster if you display multiple categories at once.

To the right, you see a sample screen of the plotter.

I have clicked the canvas a couple of times and got the yellow vertical lines.

Command-clicking
draws a red horizontal line and displays the respective y-value (depending on the radio button you have selected).

Ctrl-Clicking or changin any radiobutton or checkbox redraws the plots and erases all lines.