I've watched the excellent video made by w2aew here:
I have a question that I don't think was properly addressed: At around 12:30, when adjusting the trimmer cap and the square wave becomes rounded, that's because higher frequencies are attenuated more than lower ones.
Ok, that's pretty straightforward. But what exactly happens when he turns the cap the other way and the square wave becomes pointy? The voltage overshoots above and below the original 0 to 5 Volts of the test signal.
What exactly causes this overshoot?