Let's say I run some type of a factory and I've studied my operations and I'm able to figure out how my cost varies as a function of quantity over a week, on a weekly period. And so to visualize that, let me draw it, draw this cost function. So this is my cost axis. This right over here could be my quantity axis. So that's quantity or Q, my Q axis. Let me just call that Q. That's my Q axis.