is a collection of useful tools for process monitoring. these tools include control charts,check sheets,pareto diagrams,histograms,cause and effect diagram,defect concentration diagrams,and scatter diagrams.control charts are widely used tools to monitor assignable causes in process parameters.A control chart that depends on the distributional assumption (such as normality) is known as a parametric chart. in practice, it is quite hard to meet these strict assumptions. in such situations,non-parametric control charts are used that do not depend on the underlying distribution of the variable of interest.