syque.com

The Psychology of Quality and More

| Menu | Books | Share | Search | Settings |

Calculation detail for X-bar/R Control Charts

 

  1. Calculate basic averages (X- bar) from measured values, averaging the values in each subgroup and also measuring the range, R (the maximum minus the minimum values in the subgroup). Then average these averages to give the grand average (X-double bar) and the average range (R-bar). The grand average and the average range give the central ‘average’ line in the X-bar and the R charts.

  2. Calculate upper and lower control limits for each of the two charts. This requires the use of a ‘magic’ constants, A2, D3 and D4, which are simply looked up in the table, based on the number of measures in each subgroup. The control limits are calculated then using the formulae as in Fig. 2.

  

 Calculating X-bar/R control limits

 

Next time: Calculation detail for X-bar/S Control Charts

 

This article first appeared in Quality World, the journal of the Institute for Quality Assurance

 

Site Menu

| Home | Top | Settings |

Quality: | Quality Toolbook | Tools of the Trade | Improvement Encyclopedia | Quality Articles | Being Creative | Being Persuasive |

And: | C Style (Book) | Stories | Articles | Bookstore | My Photos | About | Contact |

Settings: | Computer layout | Mobile layout | Small font | Medium font | Large font | Translate |

 

You can buy books here

More Kindle books:

And the big
paperback book


Look inside

 

Please help and share:

 

| Home | Top | Menu |

© Changing Works 2002-2015
Massive Content -- Maximum Speed