Accum2.var degrees of freedom inconsistency in margins

[eoincondron]

I noticed the when calculating var (and std) with Accum2 that the value in the margin at the intersection (corresponding to the var of the entire dataset) is based on 0 degrees of freedom while the values in the rest of the result are based on 1 degree of freedom. Notice here that the 7.7 value in the bottom right is incorrect as it corresponds to np.var(values, ddof=0).