BS ISO 7870-9:2020 pdf free.Control charts.Control charts for stationary processes. BS ISO 7870-9 Many statisticians and statistical process control practitioners have found that autocorrelation in process data has an impact on the performance of the traditional SPC charts. Similar to autocovariance (see 3.1.1), autocorrelation is internal correlation between members of a series of observations ordered in time. Autocorrelation can be...