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? So maybe we can think of it this way, so our denominator, we want what percentage of the total variation in y? So let me write it this way. Let me call this as the squared error from the average.