Machine Utilisation

Utilisation is operating time over available time. Six hours of running in an eight-hour shift is 75%. The arithmetic is trivial and the argument is entirely about the denominator: calendar hours, scheduled hours, staffed hours, or hours net of planned maintenance. The same machine can honestly be reported at 40% or 85% depending on which one you pick, and both numbers will be defended vigorously.

The deeper trap is treating high utilisation as the goal. Queueing theory is unambiguous here: as utilisation approaches 100%, waiting time rises toward infinity, and the rise is steep well before the end. A resource run at 90% has roughly nine times the queue of one run at 50%. That is why a plant that pushes every machine toward full utilisation gets longer lead times and more work in process, not more output.

Utilisation is worth maximising on exactly one machine, the bottleneck, and worth deliberately leaving slack on all the others. Goldratt built The Goal around that single point. An hour lost at the bottleneck is an hour lost for the whole plant, and an hour saved anywhere else is a mirage.