Wouldn't it be easier to take the reference point from the base of the deck, as this can never vary? Measuring from the top will require the discard tray always to remain the same height, and if one is replaced it's back to the drawing board.
I've looked at tracking blocks of cards, and the techniques for doing so but haven't started out on this - yet! Still practising with this counting stuff.
Where I have played, the nice young lady dealing did a shuffle up on six decks right in front of me (box 3 counting from 1st), and I did think it would be reasonably easy to track a block with a bit of practice. Although she riffled four blocks of approx one and a half decks each, pulled them together, and got someone to cut them, it did occur to me that they hadn't really been shuffled up at all - just arranged in a different order. Needless to say the crap run prior was replicated in the next shoe, with a block of pictures (around a dozen) coming out later on - the running count was at +18 with less than three decks to go, and I still didn't pull a single winning hand!
Newb99