But what is that slope telling us? Well, the slope is the change in our cost divided by the change in our quantity. And it's the slope of the tangent line. This is what we first learned in calculus. As we get to smaller and smaller and smaller changes in quantity, we essentially take the limit as our change in quantity approaches zero. That's how we get the instantaneous change. So one way to think about it, one way to think about it is this is the instantaneous, this is the rate right on the margin at which our cost is changing with respect to quantity.