Statistical Process Control (Process Behaviour Charts)

Every metric wiggles. The question that matters is never "did the number change?" — it always changed — but "did the process that generates the number change?" Statistical process control answers that one question, and answering it wrong is expensive in both directions: chase routine noise and you waste investigation time (and often make the process worse by tampering); dismiss a real shift as noise and you miss the regression, the fraud, the failing pump.