This right here is the b axis. That is the b axis. Let me continue the m axis and let me continue the b axis. And then you can imagine the vertical axis here to be the squared error. This is the squared error of the line axis. So for any combination of m and b's, if you're in the mb plane, you pick some combination of m and b, you put it into this expression for the squared error of the line, it will give you a point. If you do that for all of the combinations of m's and b's, you're going to get a surface.