# Gauge R&R Calculator for Inspection Equipment in SAP QM

> Source: https://netray.co/tools/sap-qm-gauge-rr-study-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Combine repeatability, reproducibility and part variation into %GRR, %tolerance and distinct categories.

## Category

quality

## Erp

SAP S/4HANA

## Audience

- Quality engineer
- Metrology
- SAP QM consultant

## Tool

**Kind:** calculator

**Inputs:**

#### Repeatability (EV), standard deviation

**Key:** ev

**Type:** number

**Default:** 0.004

**Min:** 0

**Step:** 0.0005

**Help:** Equipment variation, same operator and part.

#### Reproducibility (AV), standard deviation

**Key:** av

**Type:** number

**Default:** 0.003

**Min:** 0

**Step:** 0.0005

**Help:** Appraiser variation between operators.

#### Part variation (PV), standard deviation

**Key:** pv

**Type:** number

**Default:** 0.02

**Min:** 0.0001

**Step:** 0.001

**Help:** Variation between the study parts.

#### Tolerance (USL - LSL)

**Key:** tol

**Type:** number

**Default:** 0.2

**Min:** 0.0001

**Step:** 0.01

**Outputs:**

#### GRR (combined gauge sigma)

**Key:** grr

**Expr:** sqrt(pow(ev, 2) + pow(av, 2))

**Format:** decimal

#### Total variation (TV)

**Key:** tv

**Expr:** sqrt(pow(grr, 2) + pow(pv, 2))

**Format:** decimal

#### %GRR of study variation

**Key:** pct_sv

**Expr:** grr / tv * 100

**Format:** percent

**Primary:** true

#### %GRR of tolerance (6 sigma)

**Key:** pct_tol

**Expr:** 6 * grr / tol * 100

**Format:** percent

**Primary:** true

#### %Contribution

**Key:** contrib

**Expr:** pow(grr, 2) / pow(tv, 2) * 100

**Format:** percent

#### Number of distinct categories

**Key:** ndc

**Expr:** floor(1.41 * pv / grr)

**Format:** integer

**Chart:**

#### %GRR as repeatability worsens

**Type:** line

**X:** ev

**From:** 0.0005

**To:** 0.02

**Steps:** 40

**Series:**

- pct_sv
- pct_tol

**Disclaimer:** Uses standard deviations from a completed study. For the study design and ANOVA itself use your MSA software or the AIAG MSA manual.

## Content

**Intro:** Capability numbers are only as honest as the gauge that produced them. A Gauge R&R study splits variation into the instrument, the operator and the parts. This calculator combines the components you already have into the three decision metrics.

**Sections:**

#### How to use it

**Body:** Run your study with 10 parts, 3 appraisers and 2 or 3 trials, then enter the repeatability (EV), reproducibility (AV) and part variation (PV) as standard deviations. Enter the tolerance for the characteristic. The result gives %GRR of study variation, %GRR of tolerance and the number of distinct categories (ndc). The chart shows how quickly a worsening gauge pushes the percentages up.

#### Formulas

**Body:** GRR = sqrt(EV^2 + AV^2). Total variation TV = sqrt(GRR^2 + PV^2). %GRR of study variation = GRR / TV. %GRR of tolerance = 6 x GRR / tolerance. ndc = 1.41 x PV / GRR, truncated to an integer. These follow the AIAG convention. Some tools use 5.15 instead of 6 for the spread, so confirm which one your customer wants.

**Bullets:**

- Below 10 percent: generally acceptable
- 10 to 30 percent: conditionally acceptable depending on the application and cost
- Above 30 percent: not acceptable, improve the gauge or method
- ndc of 5 or more is the usual minimum

#### Link to SAP QM

**Body:** In SAP QM, inspection equipment and test equipment are managed as PRTs (production resources and tools) and tied to calibration inspections. The study result belongs in your quality records, and a gauge that fails MSA should be blocked or flagged for the characteristics where it is used, so the master inspection characteristic is not recorded with an unsuitable instrument.

#### Common mistakes

**Body:** Using parts that do not cover the process range, which understates PV and overstates %GRR, using a resolution too coarse for the tolerance, and treating a passing %GRR as proof of accuracy. MSA also does not test bias or linearity, which need separate studies.

**Cta:** We can help link calibration status, PRT usage and MSA outcomes in SAP so the inspector sees only valid gauges.

**Faq:**

#### Which percentage should I use, study variation or tolerance?

**Answer:** Use the one that matches the purpose. %GRR of tolerance is relevant for product acceptance, while %GRR of study variation matters when you analyse the process.

#### Why is ndc truncated?

**Answer:** The distinct category count is a whole number of groups the gauge can reliably separate, so partial categories do not count.

#### Can I enter variances instead of standard deviations?

**Answer:** No. Enter standard deviations. If you hold variances, take the square root first.

#### How many parts do I need?

**Answer:** Ten is the common minimum, chosen to span the process range. Fewer parts reduce the reliability of the PV estimate.

## Search terms

gauge r&r calculator, grr calculator, msa gauge study calculator, ndc number of distinct categories calculator, %grr of tolerance, measurement system analysis calculator, SAP QM inspection equipment calibration

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