Well, if we think about it visually, we know that we can think about the derivative as the slope of the tangent line. So for example, that's the tangent line when Q is equal to 100. So the slope of that tangent line is, you could view as C prime, or it is C prime of 100. 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.