Think of a line graph where the line stays somewhat flat and low to the ground for a while (but still upsloping, nondecreasing) and then starts to arc up.
I'm trying to figure out a way to "characterize" these kinds of lines (when does this "hard arc" point occur, how hard is the arc, etc). Please ask questions if I am not being clear.
I tried to draw an example of what I mean https://i.stack.imgur.com/Z7HWe.png
For example I should be able to have a model equation that describes a line like this, and based on whatever such coefficient I can say "This coefficient means the arc starts to occur sooner" or "This coefficient means the arc, when it occurs, is rather strong." Does this make sense?

