gage repeatability

**Gage Repeatability** is the **variation in measurements when the SAME operator measures the SAME part multiple times with the SAME gage** — also called equipment variation (EV), it measures the pure instrument precision, excluding any operator influence. **Repeatability Assessment** - **Method**: One operator measures the same part 10-30 times — calculate the standard deviation of repeated measurements. - **EV**: $EV = ar{R} / d_2$ (using range method) or directly from ANOVA — the repeatability standard deviation. - **Sources**: Gage resolution, mechanical precision, environmental sensitivity (temperature, vibration), and sample positioning. - **Units**: Same units as the measured parameter — or as a percentage of tolerance. **Why It Matters** - **Baseline**: Repeatability is the MINIMUM measurement uncertainty — reproducibility and other factors add more. - **Resolution**: If repeatability is poor, the gage may lack sufficient resolution — need a better instrument. - **Semiconductor**: CD-SEM repeatability must be <0.5nm for advanced node CD measurements — extremely demanding. **Gage Repeatability** is **the instrument's consistency** — how well the measurement tool reproduces the same result when measuring the same item repeatedly.