1. What is Process Capability (Pp)?

Process Capability (Pp) is a statistical measure that compares the variability of a process to its specification limits. It indicates how well a process can meet specifications when the process is centered between the upper and lower specification limits.

2. How Does the Calculator Work?

The calculator uses the Process Capability Pp formula:

Where:

• \( USL \) — Upper Specification Limit
• \( LSL \) — Lower Specification Limit
• \( \sigma_{long} \) — Long-term standard deviation

Explanation: The numerator represents the specification range, while the denominator represents the process spread (6 standard deviations).

3. Importance of Pp Calculation

Details: Pp helps determine if a process is capable of meeting specifications and is crucial for quality control and process improvement initiatives.

4. Using the Calculator

Tips: Enter the upper and lower specification limits and the long-term standard deviation. All values must be valid (standard deviation > 0).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between Pp and Ppk?
A: Pp measures potential capability assuming the process is centered, while Ppk considers process centering.

Q2: What are good Pp values?
A: Generally, Pp ≥ 1.33 indicates a capable process. Higher values (≥1.67 or ≥2.0) are often required for critical characteristics.

Q3: When should I use Pp vs short-term capability indices?
A: Pp uses long-term variation and is appropriate for assessing overall process performance over time.

Q4: How is σ_long different from σ_short?
A: Long-term variation includes all sources of variation (between subgroups, within subgroups, over time), while short-term typically measures within-subgroup variation.

Q5: Can Pp be negative?
A: No, Pp is always positive since it's a ratio of positive values (USL > LSL and σ > 0).