I am preparing a write-up on these. Since my machine does not have live tooling, I cannot experiment on the machine for analyzing how the cycles behave. I have to depend on Fanuc manual only which is often not very clear. So, I have a few basic questions:

1. M51 is given to be for C-axis index mode ON. Is the number 51 always same on all the machines or do we specify a desired number in some parameter?

2. With M50 (C-axis index mode OFF), M03 would start the main spindle, and with M51, it would start the live spindle. Correct?

3. M31 (for C-axis clamp) must necessarily be used with these cycles, even in repeated calls in subsequent blocks. Correct?

4. The manual gives this syntax (apparently for G-code system A, since U, H and W are there) :
G83 X(U)_ C(H)_ Z(W)_ R_ Q_ P_ F_ K_ M_;
It further explains that
Z_ is the distance from R-point to the bottom of the hole,
R_ is the distance from the initial level to R-point level.
Is it correct, with reference to G-code system A?
If yes, what would be the effect of W_?
I believe, the given ststements are correct in system B and C, with G91.
Please clarify.
Thanks in advance.