Yes, correct: it is a cross product, not the dot product to calculate the normal.
I rushed that last post so I should really explain that I do not use the right hand grip rule to work out the surface normal. Before OpenGL became "the standard", it was common to use clockwise vertex order to achieve normal calculation for backface removal. X-Sharp, the first 3D library I ever worked with, followed clockwise sequence which the right hand grip rule doesn't apply.
For that reason, I've never relied on the right hand rule. I used the calculated normal. That's not because I'm more hardcore than you, I'm just old and was around when we used the clockwise vertex sequence, so I learned a different way. That's all.
Like I said, I need to go back and fix that section. It's pretty scrappy and I clearly wasn't thinking when I did that drawing because I just "labelled" the 3 points rather than think about what I was trying to say.
Cheers
Simon
