I bought a used 6" Jet jointer some time ago, and it's the 40th anniversary addition, so it's was made sometime around the late 90s. The jointer is actually in like new shape, doesn't appear to have much use. Anyway, it came with a patented "Magnetic knife setting jig" for Jet 6" and 8" jointers. It's in my shop, but I pulled up a picture off the internet of what it looks like:
image.jpg

On the box it says that this jig is accurate to .001". I never changed blades yet or even use the jointer, so I've never tried it. From some research, and from the Robert Vaughn (or whatever his name is) knife setting video, I heard these jigs don't work, because the blade rises when you tighten the screws. I question this though, because like I said, this is a Jet patented product (no longer produced) and claims to be accurate within .001". Anyone have experience with these?