No wonder the paper keeps falling off

This is an excerpt from a chart of the width of rolls of paper being placed onto printing machines that are producing statements sent to customers.

The supervisor is concerned that variation in the width of the rolls is a cause of breakdown where the paper becomes parted from the tractor reels feeding the paper through.

He has carried out a small experiment measuring at randomised intervals along the roll. The shift in the data is very interesting, and represents different rolls. Not only do the rolls differ in average width, they are nominally supposed to be 440mm wide, so it appears the manufacturing process isn't centred. If this happens regularly, no wonder the paper feed keeps failing,

He resolved to work with the suppliers to reduce the variation between rolls, and therefore reduce the amount of printer downtime.