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What is it: Studies of repeatability and reproducibility are called Gage Repeatability and Reproducibility studies or GR&R for short.

  • Repeatability is the variation in measurements obtained when one person measures the same unit with the same measuring equipment. Or repeatability looks at the variation between measurements of the same part when measured by the same appraiser with the same measurement device.

  • Reproducibility is the variation in average measurements obtained when two or more people measure the same parts or items using the same measuring technique. Or reproducibility is the difference in measurements between appraisers.

What is it used for: To determine the variation in the measurement system due to the measurement equipment itself and its use by the appraisers. The variation from the test equipment is called Repeatability. A good way to think about repeatability is that it is the variation we get when we measure the same part a number of times with the same measuring device. Reproducibility variation is the uncertainty, or variation, we get between people who are measuring the same parts with the same gage. Many times this is the largest source of measurement system variation. GR&R (Gage Repeatability and Reproducibility) studies are used to evaluate the level of variation due repeatability and reproducibility.

Why use it: Measurement System Analysis (MSA) is a vital component for many quality improvement initiatives. It is important to assess the ability of a measurement system to detect meaningful differences in process variables. R&R Studies are the most widely used techniques for evaluating the variation in a measurement system and determining if the measurement system is acceptable for use. Once a measurement system is found acceptable, it is equally important to institute a formal system to manage the measurement system to ensure that it continues to be reliable and dependable. Use of structured GR&R techniques with a comprehensive calibration system for measurement devices is the only way to avoid the rubber ruler syndrome.

Where to use it: Gage repeatability and reproducibility (R&R) study can be applied in most manufacturing-related measurement systems. It may be used as:

  • A criterion for judging new measuring equipment.
  • A comparison among measuring devices.
  • A means for improving performance of measuring instruments.
  • A comparison for measuring equipment before and after repair.
  • A required component for calculating process variation and the acceptability level for a production process.
  • A measure of the need for training in how to use measuring instruments.

When to use it:

  • Before implementing SPC techniques or conducting designed experiments to verify that a sound measurement system exists.
  • Periodically to ensure the measurement system has not degraded.

How to use it: The key to a good GR&R study lies in the upfront planning. A GR&R study can be planned using the following 5 steps:

  1. Define the objective of the study.
  2. Define the components of the study.
  3. Make the measurements.
  4. Calculate the %GR&R.
  5. Take action to improve the measurement process.

Important Notes

  • Most common GR&R Techniques are for non-destructive testing of variable-data measurement devices. The techniques must be modified for destructive testing and for attribute-data measurement devices.

  Name
Format
Preview (Click to enlarge)
  Variable Gage R&R sheet page 1. Template will advise whether the MSA is acceptable and whether the gage discrimination is also acceptable.
Microsoft Excel Format
Microsoft Excel
Format
Variable Gage R&R
  Variable Gage R&R sheet page 2. Template will advise whether the MSA is acceptable and whether the gage discrimination is also acceptable.
Microsoft Excel Format
Microsoft Excel
Format
Variable Gage R&R
  Variable Gage R&R sheet page 1 completed example.
Microsoft Excel Format
Microsoft Excel
Format
Variable Gage R&R
  Variable Gage R&R sheet page 2 completed example.
Microsoft Excel Format
Microsoft Excel
Format
Variable Gage R&R
 

Attribute Gage R&R sheet page 1.

Microsoft Excel Format
Microsoft Excel
Format
Attrubute Gage R&R
 

Attribute Gage R&R sheet page 2.

Microsoft Excel Format
Microsoft Excel
Format
Attrubute Gage R&R
USD $19.95
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