Control Chart Calculator for Variables (Continuous data)

(Click here if you need control charts for attributes)

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.

More about control charts.

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.

Please supply the following information
Monitored parameter Process mean (μ)
Process variability (σ)
Both mean and variability
Enter the type of control chart(s) you need. Variability is also known as "spread".
Target mean (or an estimate) Only needed for monitoring the process mean.
Sample size (n) The number of items to be sampled at each time point. Must be greater than or equal to 2.
Is the standard deviation (σ) known? Yes, σ =
No, but I have S
No, but I have R
S and R are calculated from samples taken while the process is known to be in control. S is the average of the standard deviations of these samples. R is the average of the ranges of these samples.
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