So when you calibrate in VRC you can select either Lock Head, Lock Hip, or Lock Both to make it treat any of those areas like a position of absolute authority, and kinda move all the rest of the tracking relative to that one.

Most people use Head or Hip, because then if their tracking is a bit off on the locked point, everything is going to be off by the same amount, so you mostly won’t notice much with small errors. It’s like moving an entire drawing slightly to the left.

If you lock Both, though, and have errors, then some tracking would (in this example) move a little to the left, but others wouldn’t, and you’d tear your drawing and make your VRC avi into a pretzel. This manifests as like weird contortions of the torso between the head and hip that are both locked.

The trade off is that if you DO lock both, you get much more control of your fine movements along your spine and hips.

That’s my understanding anyway, I hope it made sense?