Originally Posted by
spar
OK, I know the "Bit" in TUBOW is not very specific, but it should have been obvious that it doesn't stand for "plank". Get a block that will stand up on its own. Also, it'll help if it's a bit taller.
Once that's done, make sure you touch it 1/3 of the way down and then keep your knee there for the rest of the way down without knocking it over.
Also, please don't use wandering camera work. Re-read the stickies about the angles that are most helpful for the squat, and film each work set from a different helpful angle.