If h is a little bit smaller, I'd be finding the slope of that line. So as h approaches 0, I'll be getting closer and closer to finding the slope of the line right at my point in question. Obviously, if h is a large number, my secant line is going to be way off from the slope at exactly that point right there. But if h is 0.0000001, if it's an infinitesimally small number, then I'm going to get pretty close. So what happens if I take the limit as h approaches 0 of this? So the limit as h approaches 0 of my secant slope of, let me switch to green, f of x naught plus h minus f of x naught, that was my change in y, over my change in h, which is my change in x. And now just to clarify something, and sometimes you'll see it in different calculus books, sometimes instead of an h, they'll write a delta x here, where this second point would have been defined as x naught plus delta x.