Hawkins DM, Olwell DH (1997) Cumulative sum charts and charting for
quality improvement. Springer-Verlag New York. ISBN 0-387-98365-1 p 47-74
Reynolds Jr. MR and Stoumbos ZG (1999) A CUSUM Chart for Monitoring
a Proportion when Inspecting Continuously. Journal of Quality Technology
vol 31: No. 1. p.87 - 108