On the cumulative squares and cumulative variance quality control schemes

This paper discusses the cumulative squares and cumulative variance schemes for quality control charts. These schemes correspond to the EWMS and EWMV proposed in MacGragor and Harris (1993). Based on the distributions of the chart statistics, the average cumulative squares and average cumulative variance schemes are discussed to get the constant width between control limits and horizontal control limits. The Box quadratic form and approximation can be used to deal with the complex of cumulative variance where the means vary over time.