Square it. And then divide by the total number of data points you have. Now we get to the interesting part, sample variance. There are several ways where, when people talk about sample variance, there are several, I guess, tools in their toolkits, or there are several ways to calculate it. One way is the biased sample variance, the non-unbiased estimator of the population variance. And that's denoted, usually denoted, by S with a subscript N. And what is the biased estimator? How would we calculate it?