Fundamentals of Gage R&R

Before cutting an expensive piece of granite for a countertop, a good carpenter will first confirm that they have measured correctly: acting upon faulty measurements could be costly.

While no measurement system is perfect, we rely on them to collect data to control quality and monitor changes in critical processes. So, how do you know whether the changes that you see are real and not just the product of a faulty measurement system? After all, if you can’t trust your measurement system, then you can’t trust the data that it produces.

Minitab’s Gage R&R study can help you to identify problems with your measurement system, which allows you to trust your data and to make real improvements in your processes.

What can gage R&R do for me?

Gage R&R studies can tell you if inconsistencies in your measurements are too large to ignore—whether due to a faulty tool or to inconsistent operation of a tool.

Reveal an inconsistent tool

A company conducts a gage R&R study before using a control chart to monitor the fill weights of cereal boxes.

average vs spread

The gage R&R results show that even when the same person weighs the same box on the same scale, the measurements can differ by several grams, which indicates that the scale is in serious need of recalibration. The faulty scale would have rendered the control chart virtually useless. Although the average measurements are not far apart, the spread of the measurements is huge!

Highlight operator differences

To meet increased demand, a company hires new workers to prepare carefully-measured amounts of a costly solution. The company uses a gage R&R study to compare the new operators to experienced operators.

experienced vs new

The study reveals that, when workers measure the same sample, the measurements of new hires are too high or too low more often than the measurements of experienced workers. The company decides to conduct more training for the new hires.

How to analyze a gage R&R study in Minitab

Awareness of how well you can measure something can have substantial financial benefits. Minitab makes it easy to analyze how precise your measurements are.

employee measuring soup temperature

A restaurant plans to evaluate how it measures food temperature to ensure that the food is hot enough. Inaccurate temperatures can result in discarding good food, failing a health inspection, or even making a customer ill.

Reproduced With Permission

Getting started

Preparing to analyze your measurement system is easy because Minitab’s Create Gage R&R Study Worksheet can generate a data collection sheet for you. The dialog box lets you quickly specify who takes the measurements (operators), which item they measure (parts), and in what order the data are to be collected.

create worksheet dialog box
  1. Choose Stat > Quality Tools > Gage Study > Create Gage R&R Study Worksheet.
  2. Specify the number of parts, number of operators, and the number of times the same operator will measure the same part.
  3. Give descriptive names to the parts and operators so that they’re easy to identify in the output.
  4. Click OK.

The main event

After you enter the measurements in the worksheet, you can use Gage R&R Study (Crossed) to analyze the measurements.

crossed dialog box
  1. Choose Stat > Quality Tools > Gage Study > Gage R&R Study (Crossed).
  2. In Part Numbers, enter Parts.
  3. In Operators, enter Operators.
  4. In Measurement Data, enter 'Food Temp'.
  5. Click Options.
  6. Enter your specification limits. In this case, enter a lower specification for the minimum food temperature.
  7. Click OK in each dialog box.
soup temperature vs employee graph

The study reveals that Morgan’s measurements are lower than Taylor’s or Robin’s. Identifying and eliminating the source of the difference will improve the measurement system.

Morgan, Taylor, and Robin suggest that the hardest part of measuring soup temperature consistently is measuring soup from the same depth in the pot, so marks are added to ladle handles to make depth easy to determine.

Putting gage R&R studies to use

Taking measurements is like any other process—prone to variability. Reducing this variation with Minitab’s Gage R&R tools ensures that you can trust your measurements. The Create Gage R&R Worksheet tool makes evaluating your measurement system easier than ever.

When you evaluate your measurement system, you can have confidence that you can trust your data.