Moving span

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The quality management are moving spans ( English moving ranges ) according to a special procedure calculated span values , which for guiding the ImR card (individuals and moving range chart) , a particular type of control chart , are required.

Calculation method

With the ImR card, each sample comprises only one value. It is therefore not possible to calculate the sample range (difference between the largest and smallest sample value) for each sample, as is usual with the normal XbarR card . Instead, the most recent (usually 2 to 4) individual values ​​are summarized, their range is calculated and the calculated value is then entered in the range track of the control chart.

This means that each individual value is included several times in the calculation of the moving range; Extremely high or low individual values ​​will therefore influence several range values depending on the selected sample size .

literature

  • Edgar Dietrich, Alfred Schulze: Statistical procedures for machine and process qualification . Carl Hanser Verlag, Munich / Vienna 2005, ISBN 3-446-22894-2 .