Sum Chart Cusum

A cusum chart is a very useful technique for establishing a gradual change or trend. The technique is readily adapted to a continuous process and permits retrospective corrective action to be taken. A target mean (k) is selected, normally the average, and the difference between the target mean and the value is determined and the cumulative sum c is calculated  

each sum is obtained from its predecessor by the simple operation of adding on the new difference (x —A ) (Table 18.7). The cumulative sum is plotted against the sample 

A cusum chart is very useful to indicate, say, when an HM furnace element is coming towards the end of its life, or there has been a change in the precursor. 

---