Specification Limits (USL, LSL)
Tolerance limits set by the customer or designer — the reference base of any process capability measure.
Also known as: specification limits, USL, LSL, tolerance
Specification limits define when a characteristic is still acceptable or already defective. They differ fundamentally from a control chart's control limits:
- USL (Upper Specification Limit) — upper tolerance, from requirement/drawing
- LSL (Lower Specification Limit) — lower tolerance
- Nominal / target — optimum value inside the tolerance
- Tolerance width T = USL − LSL
- One-sided spec — only USL or LSL is set (e.g. "strength ≥ 500 MPa")
See also
Used in
In the Algorithm Lab
Sources
- AIAG — Statistical Process Control (SPC) Reference Manual, 2nd Edition
- Montgomery, D. C. — Introduction to Statistical Quality Control, 8th Edition