Normal distribution : Steel R.G.D., Torrie J.H., Dickey D.A. Principles and
Procedures of Statistics. A Biomedical Approach. 3rd. Ed. (1997)ISBN 0-07-061028-2 p 67-76

CUSUM : 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

Computer program to calculate CUSUM decision limits can be downloaded from
http://www.stat.umn.edu/cusum/software.htm

Hawkins DM (1992) A fast accurate approximation for average run lengths
of CUSUM control charts. Journal of quality technology 24:1 (Jan) p 37-43 (this is the algorithm
used by this page.