The average was just a ghost. The plant was either choking or starving, never steady.
Dr. Elara Vance stared at the raw tonnage report from the new crushing circuit. The number was good—really good. Throughput was up 12% from last quarter. Her phone buzzed with a congratulatory text from the mine manager.
“For the last six hours,” she said, pointing to a string of seven points all below the centerline, “we have been running fine. But this run of seven points all below the mean? That’s a Nelson Rule violation. It’s not out of control statistically, but the probability of this happening by chance is less than 1%. It’s a trend. The mill is grinding finer because the new media supplier’s ball hardness is different. We need to back off the feed rate now—not in two hours.” Statistical Methods For Mineral Engineers
Gus blinked. “Speak English.”
“Here to fix what ain’t broke, Doc?” he grunted. The average was just a ghost
“You’re chasing your tail,” she said. “The crusher power draw spikes, you back off. It drops, you tighten. But the lag in your feedback means you’re always reacting to what happened five minutes ago. By the time you fix it, the feed has already changed. You’re creating the instability you’re trying to solve.”
The daily average? It had dropped to 1,150 tonnes per hour. But the shift tonnage—the real money—was actually up 5% because the mill never stopped. Elara Vance stared at the raw tonnage report
The control room fell silent. A junior metallurgist raised a hand like a schoolboy. “So... we should intentionally lower throughput?”