Abstract

A method is provided for process monitoring by statistical measurement of level-of-defectives performance in manufacturing and other processes. Statistical performance data functions of mean-value shift and deviation ratio are plotted on an isogrammetric chart for off-line analysis or, alternatively, are entered into a computer that has been programmed with the isogrammetric format. The resultant information revels the probable process yield and is useful to certify quality of performance in direct terms of level of defectives being produced. The method is particularly useful for high-yield processes where statistical sampling and inspection methods tend to miss the relatively few defectives and statistical process control (SPC) criteria appear to indicate that a manufacturing process is "in control".