Well, remember, all this is is a slope of a line between when X is some arbitrary value. Let's say it's out here. So that would be X. This would be the point X comma F of X. And then this is the point C comma F of C right over here. So this is C comma F of C. So if you find the left-sided limit right over here, you're essentially saying, okay, let's find this slope. And then let me get a little bit closer.