Overview for Acceptance I-MR Chart

Use an Acceptance I-MR Chart to detect when the out-of-specification percentage might exceed an acceptable level, and to monitor the variation using moving ranges. Use when you have continuous data that are individual observations not in subgroups.

For example, a quality engineer monitors deviations from the target fill weight for a packaged product. The deviations are measured in tenths of an ounce. The upper specification limit is 26 tenths of an ounce above the target. The process is allowed to shift as long as no more than 1% of the output is expected to exceed the upper specification limit. The engineer measures 160 packages at appropriate time intervals and creates an Acceptance I-MR Chart.

The MR chart does not show evidence of unusual variation, so the engineer can interpret the Acceptance I chart. Two observations are above the upper acceptance control limit. These points indicate that the process shifted far enough toward the upper specification limit that more than 1% of the process output might exceed the specification limit.

Where to find this control chart

To create an Acceptance I-MR chart, choose Stat > Control Charts > Acceptance Charts > I-MR.

When to use an alternate control chart

If you can collect data in subgroups, use Acceptance Xbar-R Chart or Acceptance Xbar-S Chart.