So if you visualize it, you can imagine a line that's y is equal to the mean of y, which would look just like that, and what we're measuring over here, this error right over here is the square of this distance right over here, between this point vertically and this line. The second one is going to be this distance, is going to be this distance, just right up to the line. The nth one is going to be the distance from there all the way to the line right over there, and then there are these other points in between. This is the total variation y. Makes sense, if you divide this by n, you actually will get the, I should say this is the total variation in y, if you divide this by n, you're going to get what we typically associate as the variance of y, which is kind of the average square distance. Now we have the total square distance. So what we want to do is how much of this, how much of the total variation y is described by the variation in x?