Control chart vs run chart: median line versus 3-sigma control limits, how many data points each needs, and which to use at each project stage.
Cp shows potential capability, Cpk shows what you actually make. The gap reveals off-centering you can fix for free, with a worked example and verdict.
X-bar R or X-bar S chart? The deciding input is subgroup size. Why the range loses efficiency as n grows, with a worked example and a verdict by role.
c-chart vs u-chart: when each attribute chart fits, constant vs variable inspection units, 3-sigma Poisson control limits, and a clear verdict.
EWMA vs CUSUM control charts: how each detects small process shifts Shewhart misses, ARL comparison, design parameters, and which to pick.
Statistical process control vs inspection: where prevention beats detection, where 100% inspection still wins, and how to choose by what you make.
Honest taxonomy of free SPC software for quality engineers — trials vs OSS vs browser tools — and which fits which use case without 30-day clocks.
Comparison of Cpk and Ppk process capability indices with worked example, formulas, and a decision table for which index to report in PPAP submissions, customer audits, and ongoing SPC monitoring. Includes diagnostic use of the Cpk-Ppk gap.