Your maintenance reporting treats every hour as an hour. Two work orders closed, two hours spent, two entries in the completion rate. As a measure of activity that is accurate. As a measure of value it is badly wrong, and the error is expensive.
The distinction
An hour lost on the constraint is lost for the whole plant. Output does not recover, the shipment moves, and the margin on that hour is gone permanently. There is no catching it up later, because later the constraint is busy being the constraint.
An hour lost anywhere else usually costs nothing at all. Assets with protective capacity upstream and downstream absorb the interruption. Work in process buffers it. The line delivers the same output it would have delivered anyway.
Same labor cost, same work order, same entry in the completion rate. Radically different value.
Most plants have been making this trade blind for years, not because anyone chose to, but because the reporting system has no field for it.
What the constraint hour is worth
On the packaging line, the case packer runs 600 bags per hour at design rate, and contribution margin is $10 per bag.
600 times $10 is $6,000.
Every hour that asset does not run at rate, for any reason at all, costs $6,000 of contribution margin. A stop costs it. A slow rate costs it. A changeover costs it. A rework pass costs it twice, once for the bad units and once for the hour spent producing them.
The reason does not change the price. That is what makes the number so useful.
What changes when the hour has a price
The backlog stops being sequenced by age. Most backlogs are ordered by when the work order was raised and how loudly someone has asked. Once the constraint hour has a price, the backlog gets ordered by which asset the work protects, and that ordering can be defended to anyone who challenges it.
The planned outage argument gets shorter. A four hour planned intervention costs $24,000 in margin. If it prevents an unplanned stop that historically runs eight hours, it protects $48,000. That is an arithmetic problem now, not a debate between operations and maintenance.
The spare part conversation ends quickly. A $9,000 part that removes a six hour wait is protecting $36,000. Inventory arguments that used to run for months resolve in one meeting once both sides are working from the same rate.
The overtime shift gets settled. An overtime shift that recovers five constraint hours returns $30,000 against a few thousand dollars of premium labor. Or it recovered nothing, and now you can prove that too, which is equally valuable.
Why this is the most useful number in the plant
Everything else in this series is built on top of it. The hidden plant figure is annual and abstract, which makes it good for getting attention and poor for making decisions. An hourly rate is operational. It works on a Tuesday afternoon, in a fifteen minute conversation, about one asset.
It is also the number that outlives the exercise. Six weeks from now the project is over, and this figure is still sitting in your head, repricing every decision that comes past you.
This week
Get contribution margin per unit confirmed by finance in writing. Multiply it by the design rate of your constraint. Write it on one line.
Then take one decision your plant made this month and reprice it. Any decision. The overtime you approved, the outage you deferred, the part you did not stock. Run it again at the real rate and see whether the answer changes.
