neither do I. But the cliff dive into calculus is the functions to calculate where a line is going. What is it approaching is the socratic methodology. What stands out to me is the multiple mentions of this being common in vector absolute value would indicate a formula (as I would see it close to a PID formula proportional/derivative/integral) of absolute value of a projection. Rate of increase or something. I have no degree, but I've dealt with things like PID and of this sort in the real world that have left me confused why 3 yrs of engineering never touched on any of it.