Gage R&R vs Type 1 gauge study
Short answer
A Type 1 study (VDA 5, Bosch Booklet 10) measures one reference part about 50 times to check the gauge’s own bias and repeatability, giving Cg and Cgk. A Gage R&R (AIAG MSA) measures about 10 parts by 2–3 operators 2–3 times each to find how much of the variation comes from the measurement system, giving %GRR and ndc. Do the Type 1 study first; if it fails, a Gage R&R makes no sense.
Side by side
| Aspect | Type 1 study (Cg, Cgk) | Gage R&R (%GRR, ndc) |
|---|---|---|
| Question | Is the gauge itself accurate and repeatable? | How much of the observed variation is the measurement system? |
| Parts | One reference (master) part with known value | About 10 production parts covering the process range |
| Operators | One | Two or three |
| Measurements | 25–50 repeats | 10 parts × 3 operators × 2–3 trials |
| Results | Cg (repeatability), Cgk (with bias), bias t-test | %GRR of study variation or tolerance, ndc, EV, AV, PV |
| Typical limit | Cg and Cgk ≥ 1.33 | %GRR < 10 % acceptable, 10–30 % conditional, > 30 % not acceptable; ndc ≥ 5 |
| Standard | VDA 5, Bosch Booklet 10 | AIAG MSA 4th edition |
What each study can and cannot see
The Type 1 study isolates the instrument: one part, one person, ideal conditions. It finds bias and poor resolution but says nothing about operator influence or how the gauge behaves across real parts. Gage R&R adds operators and part-to-part variation, so it shows reproducibility and whether the gauge can tell good parts from each other, but it does not detect a constant bias, because every operator shares it.
Recommended order
Check resolution (at least 5 % of the tolerance), run the Type 1 study, then the Gage R&R. Add a linearity and bias study if the gauge is used over a wide range, and an attribute agreement analysis for visual or go/no-go checks.