Hy,
it requires much time to see something with N=1000000.
Set N=10000, with box checked you will se a growing sinusoid. From about half graph on you'll see a slowing down.
If you put N=1000000, for example, if you have to show a temperature for many hours of acquisition, the problem will be even greater.
I have not found a way to add a piece of line without redrawing all.
Unchecking shows that when you draw a line, the preceding lines disappear.