This wizard computes the Lower and Upper Control Limits (LCL, UCL) and the Center Line (CL) for monitoring the process mean and variability of continuous measurement data using Shewhart X-bar, R-chart and S-chart.

The limits are based on taking a set of preliminary samples drawn while the process is known to be in control. The information from these samples is used to estimate the process mean and standard deviation:

- Process mean: Estimate the process mean by averaging over the set of samples, or enter the target mean (μ) if you have that value.
- Process standard deviation (σ): If you don't have a known value for the standard deviation (e.g. from historic data), compute S by averaging the standard deviations of the samples, or R by averaging across the
*ranges*of the samples. The*range*of a sample is the difference between the maximum and minimum observations.In general, S is a more accurate method.