Overall-variation index screen
Pp / Ppk performance
Inputs
User-entered two-sided lower specification limit on the same measurement basis as the mean and overall standard deviation.
User-entered two-sided upper specification limit; it must exceed the lower limit.
Leave blank to use entered mean/sigma. Otherwise paste 2–5,000 scalar values separated by spaces, commas, semicolons, or new lines; no headers, labels, or locale decimal commas.
User-entered overall process mean, not inferred from raw observations in this bounded workspace.
User-entered overall standard deviation used in Pp/Ppk, not within-subgroup sigma.
Results
Pp (overall spread index)
1.1111
—PPL (lower performance)
1.3333
—PPU (upper performance)
0.88889
—Ppk (nearest-side performance)
0.88889
—Ppk / Pp centering comparison
80
%Pp = (USL−LSL)/(6soverall); PPL = (x̄−LSL)/(3soverall); PPU = (USL−x̄)/(3soverall); Ppk = min(PPL, PPU)
A first-pass number, not a code check, certification, or approval. Read the method and its limits below. What this is and is not.
Nearby: ISO 286 fits · Tolerance stack · Position deviation · MMC bonus & virtual condition
Method
Formula, when it applies, and when it does not
Calculate Pp, PPL, PPU, Ppk, and a Ppk-to-Pp centering comparison from two-sided specification limits, mean, and overall standard deviation.
Pp = (USL−LSL)/(6soverall); PPL = (x̄−LSL)/(3soverall); PPU = (USL−x̄)/(3soverall); Ppk = min(PPL, PPU)
When
- Two-sided limits
- User-entered overall sigma
- Comparable measurement basis
- Normal-analysis context
Don’t
- This reports formula values using a user-entered overall standard deviation in a stated normal-analysis context.
- This screen does not test normality or stability, create control charts, account for measurement-system error, calculate confidence bounds, select a benchmark, recommend acceptance, or establish process or product capability.