Elara calculated the correlation coefficient between feed rate and product fineness. It was -0.85. Strong, negative, and ignored.
There, the problem was different. The mill power wasn't erratic—it was stubbornly stable. And that was worse. Because the cyclone overflow particle size (the % passing 75 microns) was drifting downward, slowly but surely. The shift supervisor kept increasing the mill feed rate to compensate, chasing the tonnage target.
The average was just a ghost. The plant was either choking or starving, never steady. Statistical Methods For Mineral Engineers
She drew a Shewhart control chart on a whiteboard in the control room. Upper control limit. Lower control limit. And in the center, the target P80 of 150 microns.
“The mean lies,” she muttered, reaching for a highlighter. There, the problem was different
She didn't celebrate. She opened her laptop instead.
Then she closed her laptop, patted Montgomery’s textbook, and smiled. Statistics didn't move rock. But they told you which lever to pull, and when to leave it alone. That was the real art of mineral engineering. Because the cyclone overflow particle size (the %
She left him with a process behavior chart and walked to the grinding mill.