The control charts consist of two graphs:
- Centering card : a chart to follow the central tendency (Individual I, Average Xbar)
- Dispersion card: a chart to follow the dispersion (Standard deviation, Range)
There are 3 types of Control charts:
- Individual & moving Range control charts: I-mR
- Average & Range control charts: Xbar-R
- Average & Standard deviation control charts: Xbar-S
By default, the Individual control chart (Ind., I-mR) will be selected. In the “Card” column, you can change the type of card regarding your process need.
To compute LCL and UCL (LCI and LCS in French), we use standard Shewhart approximations as described in Pillet M. "Appliquer la maîtrise statistique des processus MSP/SPC".
Individual & moving Range control chart - I-mR (Ind.) :- To determine how the process changes over time
- For continuous data
- Data not collected over subgroups
Average & Range control chart - Xbar-R:- To determine the process variation over subgroups
- Data collected over subgroups
- Sample size <10
Average & standard deviation control chart - Xbar-S:- To determine the process variation over subgroups
- Data collected over subgroups
- Sample size >10
