# Control Chart Calculator for Variables (Continuous data)

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.