A variance-numerator quotient scan divides the weighted squared-deviation sum by the stated total weight, turning the fluctuation numerator into the variance row by row. The arithmetic is exact only for the stated counts or probabilities, squared deviations, numerators, quotients, and rows in the ideal ensemble model. Real systems add preparation bias, finite samples, correlations, detector/counting calibration, thermalization limits, finite precision, and measurement uncertainty.
The variance quotient is the weighted squared-deviation numerator over total weight. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The numerator is the sum of weighted squared terms
The three contributions are 4, 0, and 4. Their sum is 8.
Nσ=4+0+4=8
The denominator is total weight
The weights are 1, 2, and 1. Their total is 4.
W=1+2+1=4
Variance is numerator over total weight
Variance divides numerator 8 by total weight 4, giving 2.