I have never seen the tutorial but it is about as easy as falling off a log so I have never needed one.
Falling off a log is waaay harder. Especially if there's any altitude to the sumbich and/or rough landing zone, and you are not really into PAIN!
I can see the value if you are having to learn it from a book whilst in hospital with both arms in casts. Once you escape and actually lay-hands on a physical manifestation of an
actual 4-j independent chuck, it should come natural in a few minutes.
- First comes "Aha!", that's how the f****r works!", as you realize the obvious: that advancing one screw naturally has to have its opposite mate retract to allow room. But ONLY that much or just a smidge LESS! Backlash thing.
No joke. People FIGHT this, and for
years, when they should know better. Metals don't squeeze easily, and plastics should not be asked to do.
- then comes accurate. Mark One Eyeball, sharpish stylus, reliable source of light to gage first the gap, then the drag.
- Speed does take a while longer, largely because to become "fast" you simply have to hit it by "calibrated eyeball" really close,
first go, otherwise chase-tail, check, chase tail again, repeat.
Only ever needed a DI when I had to pick-up on an existing feature to less than a thou.
Read: "Near-as-dammit
NEVER."
DI is otherwise a time-wasting nuisance, plus risk of damage to the DI, most any "normal" work.
It ain't hard.
But one
has to go grab the chuck and
practice.
Any gadget-assisted shortcut always takes
longer.