On the use of V-mask techniques to estimate variations in Cusum control charts by using a commercial spreadsheet

The laboratories verify data from control samples through the application of typical control charts by using commercial spreadsheets. The criteria to decide whether a measurement procedure is in statistical control involves the interpretation of the control chart after each analytical run although the decision is not always practical. So, to detect long term trends in the process, a Cusum chart graphic representation can be implemented. The use of a V-mask verification tool will show the point from which the deviations are significant. Since the construction of a V-mask is complicated in practice, in this article is proposed the definition of a visual representation and also how to construct a tabular procedure with a commercial spreadsheet form in which the V-mask serves as control limits for the Cusum chart.