If in your notation xbar means the MEAN value of the series, then this sum Σ(x – xbar) is zero. This sum is ALWAYS zero for ANY finite series. Particularly, it is equal to zero for the given particular series. Original Centered values values x-xbar ------------------------------------ 7 -0.2 6 -1.2 10 2.8 7 -0.2 5 -2.2 9 1.8 3 -4.2 7 -0.2 5 -2.2 13 5.8 sum = 72 xbar = 7.2 sum = 0