Most people put the returns right first — the wrong ones came back, so that is where the work is — or mend whichever machine the bell puts them at because its heap is the biggest. Both lose: while you tidy up, the machine that made them is still making them, and once the check table is full the next wrong one goes out for good. Stop it where it starts, and find where on the machine’s last five, not on the heap. One cross is a slip; two is a machine. Every step a fault travels, more good work is built on top of it, which is why the same fault costs about ten times as much at the end of the line.