ABSTRACT
Statistical Process Control usually deals with data lots indexed in time. If we look at the mean drift model in Section 3.5 as being close to reality, then we might be tempted to look on the production process as wandering, over time, from a region of satisfactory performance, to one which is not satisfactory. If this were the case, then we might want to develop a test where an alarm sounded as we moved outside the region of satisfactory performance so that we could take corrective action.
