Elam, Matthew E., and Kenneth E. Case. “A Computer Program to Calculate Two-Stage Short-Run Control Chart Factors for (X,MR) Charts”. Journal of Statistical Software 15, no. 11 (April 13, 2006): 1–13. Accessed November 30, 2022. https://www.jstatsoft.org/index.php/jss/article/view/v015i11.