Mad. Mean absolute deviation. And what we want to do is we want to take the mean of how much do each of these data points deviate from the mean. And I know I just used the word mean twice in a sentence, so it might be a little confusing. But as we work through it, hopefully it'll make a little bit of sense. So how much does Manuela's, the number of bubbles she blew, how much does that deviate from the mean? Well, Manuela actually blew four bubbles, and four is the mean.