Which metric is used to evaluate process capability relative to specification limits?

Question

Options

• ARTY
• BCpk
• CDPMO
• DTakt time

• A
  6% (3)
• B
  88% (43)
• C
  2% (1)
• D
  4% (2)

Explanation

Cpk (Process Capability Index) directly measures how well a process fits within its specification limits by comparing the process spread and centering to the upper and lower spec limits - making it the standard metric for evaluating process capability.

• A (RTY – Rolled Throughput Yield) measures the probability that a unit passes through all process steps without defects; it evaluates quality flow, not spec limit compliance.
• C (DPMO – Defects Per Million Opportunities) quantifies defect frequency at scale (used in Six Sigma sigma-level calculations) but doesn't directly reference specification limits in a capability ratio.
• D (Takt time) is a lean/flow metric that sets the production rate needed to meet customer demand - entirely unrelated to specification limits.

Memory tip: Think of the "k" in Cpk as "keeps it centered" - Cpk penalizes a process that drifts off-center relative to the spec limits, which is exactly what capability analysis is designed to catch.

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