Learn the basics of control charts and how to use them to ... the upper and lower control limits for the mean are calculated as X-bar +/- A2*R-bar, where A2 is a constant that depends on ...

Control charts are graphical tools that help industrial engineers monitor and improve the quality and stability of a process. They show how a process variable changes over time, and compare it ...

Key Points X-bar and R charts are useful control charts for use with rational subgroups. ... In the formulas above, you see mention of the constants A2, D4, and D3.