Yes, the diagram show how I learned it and how I teach it. Some folks curl their fingers from a towards b and then stick their thumb out for axb. I also illustrate the Frenet frame with my index finger as the tangent and my middle finger as the normal.
*shows
Now that I’ve seen the “thumb first, index second” method, I think I’ll start teaching it as an alternative! It feels different, and I’m not yet sure which I prefer.
I am #TeamFingerCurl . Not for any particular reason other than thats how I was taught in high school physics.
Do you also do 3D Frénet? I first was taught (as 2nd year UG) Frénet in any dimensions and then specialized to 2 and 3, so no fingers involved.