specification limits

**Specification Limits** are the **engineering-defined boundaries that define acceptable product performance** — derived from design requirements, customer specifications, and process capability studies, specification limits define the range within which a measured parameter must fall for the product to be acceptable. **Specification Limit Types** - **USL (Upper Specification Limit)**: The maximum acceptable value — exceeding USL means the product exceeds tolerance. - **LSL (Lower Specification Limit)**: The minimum acceptable value — below LSL means the product is under tolerance. - **Bilateral**: Both USL and LSL exist — the parameter must fall within the range [LSL, USL]. - **Unilateral**: Only one limit — e.g., defect density only has a USL (lower is always better). **Why It Matters** - **Different from Control Limits**: Spec limits come from the CUSTOMER (what's needed); control limits come from the PROCESS (what's achieved). - **Capability**: The relationship between spec limits and process variation defines capability (Cp, Cpk). - **Disposition**: Product outside spec limits is rejected, reworked, or used-as-is with customer concession. **Specification Limits** are **the customer's requirements** — the engineering boundaries that define acceptable product performance, distinct from process control limits.