The R chart consists of the following:

·    The plotted points, which represent, for each operator, the difference between the largest and smallest measurements on each part. Because the points are arranged by operator, you can see how consistent each operator is.

·    The green center line, which is the grand average for the process (average of all the sample ranges).

·    The red control limits, which represent the amount of variation expected for the sample ranges. These limits are calculated using the variation within samples.

If any of the points on the graph go above the upper control limit (UCL), then that operator is having problems consistently measuring parts. The UCL value takes into account the number of measurements by an operator on a part and the variability between parts. If the operators are measuring consistently, then these ranges should be small relative to the data and the points should stay in control.

A number of the data points are "out of control," indicating that the three operators are measuring inconsistently.