Yeah, "crush depth" and "test depth" are some pet peeves for me.
Without getting into trouble, I kind of blame Tom Clancy for making them sound so important. What's
more important is figuring out a good "working depth" where you aren't wasting HP air or blowing out watertight seals.
Think of it like this- if you own a Corvette are you
always going to drive it at 140 MPH? In that same reasoning, what's the deepest you have to go so you don't cavitate at a Flank bell? Why do you need to go deeper?