discrimination

**Discrimination** (or resolution) in metrology is the **smallest change in a measured value that the measurement system can detect** — the minimum increment that the gage can distinguish, determined by the gage's resolution, precision, and signal-to-noise ratio. **Discrimination Requirements** - **Rule of Ten**: The gage should have at least 10× better resolution than the tolerance — if tolerance is 4nm, gage resolution should be ≤0.4nm. - **ndc**: Number of Distinct Categories from Gage R&R — ndc ≥ 5 is required, indicating the gage can distinguish at least 5 groups within the part variation. - **Digital Resolution**: The smallest displayed digit — but actual discrimination may be worse than displayed resolution. - **Signal-to-Noise**: True discrimination depends on the measurement noise floor — not just the display. **Why It Matters** - **SPC**: Insufficient discrimination causes "clumping" on control charts — data groups into discrete levels instead of smooth variation. - **Capability**: If the gage cannot distinguish good from bad parts, capability assessments are meaningless. - **Technology Scaling**: As semiconductor features shrink, metrology discrimination requirements tighten proportionally. **Discrimination** is **the gage's minimum detectable change** — how small a difference the measurement system can reliably detect and distinguish.