Thread milling form error

[Milling man]

I've also never found a satisfactory answer to this question: Is the ideal 60 degree thread form measured along the thread itself (at the pitch angle), or as a section along the axis of the screw, as if turned with a flat 60 degree insert?

The thread profile is normalized in a plane passing through the axis of this thread. For example - the simplest threaded cutter on a lathe.