so the running sum is going to be the next forecast error minus and here's the forecast error plus the previous forecast error, that's the running sum, the sum of all the forecast errors as we go so there's the forecast error then we do the same thing again, actual minus forecast plus previous error, sum of error, like that and i think you can figure out where this one's gonna go, we can click and drag on this too, so click and drag and now we filled, everywhere we go, we have filled this equation in properly, each one of them is the current forecast error plus the sum of all the previous forecast errors.