Here I've got a weird behavior -to me, at least- by an expression and I'd like to understand where's the mistake I made.
I wanted to have an esteem of the overall distance of a cycling course.
After drawing a mask all along the roads, I pasted it to a null's position and turned the comp's framerate to 50 for a higher accuracy.
Then I took Dan Ebbert's (thank you, your website saves my life almost daily) expression for accumulating random values and I fitted it to my need. At the end, I divided for the maps scale.
Now the fun part: the value sometimes decreases, expecially when the path bends.
My knowledge is that a curve may not be represented correctly, but it's still a vector between two points.