OPS.9:1 - Problem frame

A queue can be long because service capacity is scarce, inputs arrive in bursts, prerequisites are incomplete, acceptance is delayed, or earlier defects return as rework. Several of these mechanisms can obtain together. A resource may be idle for much of a week and still constrain a short critical window.

Here a current constraint is a supported limiting relation for one operating result under a stated arrangement and horizon. It can concern usable capacity, readiness, sequence, quality, access, a decision or another condition. It is not a permanent label attached to the busiest person or machine.