Gage Repeatability and Reproducibility
Gregory A. Hetland, Ph.D.
Hutchinson Technology Inc.
Dr. Hetland is the manager of corporate standards and measurement sciences at Hutchinson Technol-
ogy Inc. With more than 25 years of industrial experience, he is actively involved with national, interna-
tional, and industrial standards research and development efforts in the areas of global tolerancing of
mechanical parts and supporting metrology. Dr. Hetland’s research has focused on “tolerancing opti-
mization strategies and methods analysis in a sub-micrometer regime.”
This chapter shows examples of calculating capabilities for a gage repeatability and reproducibility (GR&R)
study on geometric tolerances, and identifies ambiguities as well as limitations in these calculations.
Additionally, it shows tremendous areas of opportunity for future research and development in GR&R
calculations due to past and still-current limitations in the variables considered when making these calcu-
lations. This chapter will define conditions not being accounted for in the calculations, therefore limiting
the measurement system’s capabilities.
Standard GR&R Procedure
The following is a standard procedure used for calculating a GR&R that relates to geometric controls per
ASME Y14.5M-1994. Initial analysis will focus on a positional tolerance in a nondiametral tolerance zone.
Please note: A small sample size is used only out of convenience. Small sample sizes are strongly sup-
ported when needing a quick “snap-shot” of a capability. I do not, however, promote small sizes for in-
25-2 Chapter Twenty-five
Figure 25-1 Sample drawing #1
Table 25-1 GR&R Analysis Matrix
• Given 10 parts measured twice under the same conditions
• Same procedure
• Same machine
• Same person
• Resultant Values (R.V.) are to be shown in positional form (not just x or y displacement).
• Derive the range between runs for Part 1, Part 2, ... Part 10.
• Sum the rang