I am not certain whether I am correctly using the scale on the SVD-185 turning tool fixture -- I am referring to the scale that is numbered from 0 through 5 and has geartooth-like markings. The trouble is that I can't tell from the instructions whether the numbers correspond to the valleys of the notches or to the peaks since the numbers are not clearly aligned with either ... they just sort of fall about midways between them. After a lot of looking at pictures and head scratching, I finally decided to use the valleys of the markings and to make it more visible, put a red mark in the bottom of each valley.
I know that it would not make a lot of difference if I just picked one convention and stuck with it that would make my results repeatable. However, when turning at the shop of any of my friends who also use Tormek's, I hate to change their fixture setting when one of us is off by half of a setting. It also can be a source of confusion if one person wants to duplicate the grind of another on his bowl gouge, but can't get it to look quite right because of the "peak vs. valley" controversy.
Maybe the new fixtures have markings that are clearer to interpret, but my SVD-185 is somewhere between 7 and 10 years old and, like me, getting somewhat senile.
I have been using the (peaks) as my mark. However, good question and I also await Jeff's reply on this.
Paul
As boehme has concluded, it really doesn't matter, as long as you are consistent in which you use. I use the peaks...it just seems easier to me. As for repeating another's shape, the difference from the peak to the valley would be very slight.