Refers to the monitoring of product and process data using statistical methods. A value – such as temperature – is measured over time and significant deviations are determined. A significant deviation is defined as an outlier that is outside three times the standard deviation of the mean value. In addition, upper and lower specification limits are defined by quality engineers. The distance of the measured values from the specified limits is known as the process capability number Cp. The term CpK is used when the lower and upper limits are considered on both sides. The typical representation of the values over time with corresponding limits is referred to as a quality control chart.