It is recognized that CUSUM scheme is a sequence of Wald sequential probability ratio tests (SPRT’s) which allows for the optimality properties of CUSUM procedures to be developed. Therefore, designing a CUSUM as sequence of SPRT’s suggest a different tabulation of CUSUM average run length(ARL) than has been previously published by[5] and[2].[7] showed the superiority of a CUSUM scheme for detecting a rare event over a non- CUSUM scheme.[10] also went further to include the Fast Iinitial Response (FIR) feature. The FIR feature gives a simple procedure for detecting an out-of-control situation at start-up more quickly. However, if the process is initially in control state, the FIR feature has little effect whereas if it is in an out-of-control state, a signal is given much more quickly.