So we have m groups here, and each group here has n members. So how many total members do we have here? Well we had m times n, or 9, 3 times 3 total members. So our degrees of freedom, and remember, you have this many, however many data points you had, minus 1 degrees of freedom, because if you know, if you knew the mean of means, if you know the mean of means, if you assume you knew that, then you only would, then only 9 minus 1, only 8 of these are going to give you new information, because if you know that, you could calculate the last one, or it really doesn't have to be the last one, if you have the other 8, you could calculate this one, if you have 8 of them, you can always calculate the 9th one, using the mean of means. So one way to think about it is that there's only 8 independent measurements here, or if we want to talk in terms of general, if we want to talk generally, there are m times n, so that tells us the total number of samples, minus 1 degrees of freedom. So if we were actually calculating the variance here, we would just divide 30 by m times n minus 1, or this is another way of saying 8 degrees of freedom, for this exact example. We would take 30 divided by 8, and we would actually have the variance for this entire group, for the group of 9, when you combine them.