SPC Chart

An SPC chart is a plot of data over time. It allows you to distinguish between common and special cause variations. It includes a mean and two process limits which are both used in the statistical interpretation of data. The rules: 1) Any single point outside the process limits. 2) A run of 7 points above or below the mean (a shift), or a run of 7 points all consecutively ascending or descending (a trend). 3) 2 out of 3 points within 1 sigma of the upper or lower control limit. All these rules aid interpretation but still require intelligent examination of the data. This visual highlights when a rule has been broken and highlights whether this is an improvement or deterioration