Gauge R&R

Gauge Repeatability & Reproducibility (Gauge R&R) uses a mathematical method to analyze the variation in a measurement system.

Gauge R&R uses a statistical tool called ANOVA, or analysis of variance. It allows the person conducting the testing to separate out the variation cause by the operator, the gauge itself, and the contribution by the part being measured.

Gauge R&R determines if a measurement process is repeatable, meaning if you measured the same thing several times the results would be consistent.

It also determines if a measurement process is reproducible, meaning that someone else can step in and do the measurement with the same results. Gage R&R assesses the whole system, not just the measuring device. Individual instrumentation is not checked. Rather, the use of the instruments in a specific application is assessed.

Consistent results hinge upon accurate and precise measuring devices, standard work, good training, and trained operators. While full-blown Gauge R&R responsibilities frequently fall on the quality team, anyone can use the basic principles in making sure measuring devices in processes yield consistent results.

Note: Both spellings, “Gauge R&R” and “Gage R&R” are in common use. A quick check of the dictionary shows that both spellings are acceptable.

Gauge R&R helps to ensure that you are able to get precise measurements. It does not guarantee any sort of accuracy. To get an accurate reading, you would have to calibrate your instrument by comparing it to a known standard.

Remember, precision means small variation and accurate means centered around the desired value.

Gauge R&R is a part of a comprehensive quality approach. It makes sure that the devices you are using to manage your processes do what they are supposed to. It is fairly common that different operators yield different results in a production process—the same is true when taking measurements.

Many production processes use measuring devices that are not managed within a quality program. Used incorrectly, these devices can cause problems.

Consider the example of a measuring device for cutting the wiring that goes into a harness. There are two main failure modes. The first is that the measurements vary due to a problem with the instrument. Perhaps a mount is loose, and the readings vary due to the wiggle. It would be hard for an operator to get repeatable results.

The other mode would be that operators use the measuring device differently. Each would get a different result.

The Gauge R&R Process

True gauge R&R is based on a statistical process called ANOVA, or analysis of variance. It is rather complicated and calls for substantial expertise. Most people who are not statistical gurus will be involved in one of two main ways.

1. They may be asked to help collect data so the expert can perform the analysis.
2. They will need to make sure that the devices they are using are current. Gauge R&R calls for periodic analysis. Operators need to make sure they are not using equipment with expired testing, especially if gauge R&R is required as part of a production process or for certification.

Gage R&R in Lean

The concepts of gauge R&R apply when doing data collection for continuous improvement projects, even though the math is unlikely to be used.

The data collection process should be clearly spelled out so a person can get consistent results. This might be as simple as putting a piece of tape on the floor to indicate precisely where to start timing the operator for the next work cycle.

If a second person is also timing the process, they should use the same methods as the first person. If they don’t and they record information using different steps, perhaps not starting the stopwatch for the new cycle at the same spot every time, the data can come out erratic.

Data collection processes apply to all information gathering efforts, not just when timing operators. Whether it is logging defects, measuring floor space, or recording supplier performance, a strong process is important.

Words of Warning About Gauge R&R

• Don’t try to use formal gauge R&R without training. It has some serious statistics involved and is easy to make mistakes on.
• Gauge R&R may be required as part of a contract or certification process.