Setting up a Variables Control Chart
The five steps for setting up X-bar & R
control charts are:
1. Collect and Calculate Subgroup Data
2. Calculate the
Centerlines and Control Limits
The formulas for calculating the
centerlines and control limits are given in Appendix 1. The control
chart factors you’ll need for the limits can be found in Appendix 2.
Set the scales for the charts.
Add the centerlines and control
3. Plot the Data
Interpret the Control Chart
If no points are outside the limits and
there are no unusual patterns, the process is stable.
If more than
two points are outside of the limits, it is not stable.
point is outside the limits, drop it, recalculate the centerline and
limits, and replot the data. In this case, the process is stable if
all points are within the control limits.
5. Take Action—Use the
calculated limits if the process is stable.