# Synthetic SPC investigation / Rev A

**SYNTHETIC DEMONSTRATION — fictional engineering records. No employer, customer, real equipment acceptance or supplier engagement is implied.**

Characteristic: Valve-spool outside diameter. Target 25 mm; LSL 24.9; USL 25.1.

## SPC-E01 / Gauge repeatability check

Ten repeated checks on the reference artifact span 0.003 mm; zero offset remains within the fictional gauge check limit. The scenario does not point to a gauge shift.

Interpretation: Measurement is a weaker explanation than a process change.

## SPC-E02 / Tool inspection / sample 70

Edge buildup is documented on the finishing tool. Tool use crosses the scenario service interval during the upward shift; room temperature remains close to its baseline.

Interpretation: Tool-condition change is the leading hypothesis. Correlation alone would not prove it.

## SPC-E03 / Controlled correction / samples 71–90

Tool is replaced, the setting is verified, and twenty consecutive parts return toward target. The old-tool condition is not deliberately recreated.

Interpretation: Supports the tool hypothesis. This is a limited verification run, not a completed long-term capability qualification.

Contain suspect lots SYN-302/SYN-303; do not infer full-lot defect counts from measured samples. Correct the tool condition, verify a longer stable run and update control-plan ownership. All observations are simulated.