Mean time between failures on a mixed-age line

Someone will ask for a single number. Mean time between failures is the number they were taught to ask for. On a line where three motors were replaced in 2019 and one housing is original, that mean is a peace treaty between machines that are not at peace.

What the average swallows

A pinion that only fails on a heavy grade will look healthy if you divide all hours by all stops. The operators already know the grade. The average does not.

Age is not a moral quality

New is not innocent. A poorly aligned replacement can be worse than a worn original that the millwrights have learned. We mark rebuild dates on the timeline as events, not as halos.

What we draw instead

Stops as marks on a calendar, product grade or load noted where you have it, rebuilds as vertical lines. If a cluster appears, the briefing points at the cluster. If it does not, we will not manufacture one to justify a visit.

If a consultant has already sold you a single MTBF for the hall, keep it in the quarterly pack. Do not let it choose which housing to open in March.