In a normally-distributed dataset, two modes can occasionally be obtained.

In industrial practice, control charts for mean and range (X bar R) are usually based on sample sizes of 5.

Capability index Cp takes into account the centrality of the process within the tolerance interval.

When Cp is acceptable and Cpk unsatisfactory

The mode is the appropriate measure of central tendency when the characteristic is qualitative.

Fluctuations that may affect the average level of the quality characteristic or dispersion are attributable to special causes.

A control chart for the average (X bar R) is useful when monitoring a quality characteristic measured per unit.

The total variance observed σ²_Total is the sum of  :

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The spread of the measurable characteristic, in the case of a sample of size 5, is evaluated using the moving range (range calculated from the n value and the n-1 value).