process monitoring is an ongoing activity for the improvement of the quality of products and services. All the processes exhibit variations in their output and these variations are classified into two types named as natural and un-natural. The natural variations have no special cause and are acceptable while un-natural variations are harmful and may be related to special causes. The special cause may further be classified into two categories namely persistent and transient. The effect of persistent causes remain until problem is detected and diagnosed while the effect of transient stays for a short period,then disappear/and reappear at some future time.