Now the next thing I want to think about is how many degrees of freedom do we have in this calculation how many, kind of, independent data points do we actually have, well for each of these, over here, if you know we have 'n' data points for each one, in particular n is 3 here, but if you know n minus one of them, you can always find the 'n'th one, if you know the actual sample mean. 