In the Cp/Cpk example, USL and LSL refer to what?

• A. Upper specification level and lower specification level.
• B. Upper statistical limit and lower statistical limit.
• C. Upper specification limit and lower specification limit.
• D. Useful standard limit and lower standard limit.

Answer: (C)

USL and LSL are the upper specification limit and lower specification limit. They define the acceptable range for a product characteristic as set by design or customer requirements. In Cp and Cpk, this tolerance window (USL minus LSL) is what the process spread is compared against. Cp uses the full tolerance relative to 6 sigma to show potential capability, while Cpk accounts for where the process mean sits inside that window by taking the smaller distance to either limit, reflecting actual capability given the process centering. The terminology focuses on specification limits, not statistical limits, which is why the other phrasings aren’t used in this context.