The b stands for between. So another way to think about it, how much of this total variation is due to the variation between the means, between the central tendency? That's what we're going to calculate right now. And how much is due to variation from each data point to its mean? So let's figure out how much is due to variation between these guys over here. So one way to think about it, for each of these data points, actually, let's think about just this first group. For this first group, how much variation for each of these guys is due to the variation between this mean and the mean of means?