Elara didn't argue. She pulled out a run chart—a simple time-series plot of the crusher’s closed-side setting (CSS). “See these oscillations? Every time you adjust the CSS manually, you overcorrect. The moving range between samples is 4 millimeters. Your control limit for natural variation should be 2 millimeters. You’re introducing special cause variation.”

Elara calculated the correlation coefficient between feed rate and product fineness. It was -0.85. Strong, negative, and ignored.

Elara was the site’s mineral processing engineer, but her secret weapon wasn't a froth flotation cell or a high-pressure grinding roll. It was a battered copy of Montgomery’s Introduction to Statistical Quality Control and a stubborn refusal to trust averages.