This is an awesome breakdown, very well written. I think that some of the math frames could have been made easier to understand; the notation could be overwhelming. They don't explicitly state that the 0-7 field corresponds to bits in a byte, so this frame could be interpreted as nonsense to someone who didn't get that, when in reality it's pretty simple stuff:
[edit] their choice of 0xb for the low four bits a few frames later is also confusing, since they used the same character as a variable earlier. They could have clarified that by using B instead of b.