Statistical process control (SPC) charts are crucial for process stability, especially with improved data collection. Introduced by Walter Shewhart in the 1920s, SPC uses random samples to estimate statistics and assess variation. With better data availability, techniques like the Rbar method, which estimates standard deviation using subgroup ranges, need reevaluation.

This article highlights the use of linearity and bias studies to extract information on the accuracy of measurements, highlighting instruments that may need further investigation.