Always wondered what, exactly, the PLEK machine does, and doesn't do, and so for me, this was interesting as it walks you through the process. It is a tool, and can be used improperly, like any other too, but can be great if used correctly by a skilled operator. For those of you that do your own fret levelings, there is a part where he talks about the machine taking readings with neck under stress from string tension, and one without, and doing the math to determine what to do to the frets with strings off, to make it right under tension. So how does one determine the difference doing it manually? Sorry never did any fret work, so if this is a silly question, my apologies.