ABSTRACT
Automatic temperature controls are activated only when there is a difference between the actual and the desired temperature, and temperature fluctuations are inevitable. The chart, with its upper and lower control limits, and individual measurements plotted in the order of production is known as a control chart. The control chart is useful for separating the “only to be expected” variation from that which indicates a change in the process. A process is overcontrolled when corrections are applied on the basis of extreme values when those extreme values are actually perfectly normal to the process. Control charts supply an excellent means of recording routine quality data and form a sound basis for performance review and quality improvement programs. The natural tolerance of a given process refers to the numerical width of the band of the expected variation of individual results when the process is operating in statistical control.
