By the time the control phase is reached, there may have been several improvements made and revisions required until a sustainable improvement is able to be achieved within the previous improve phase. The new improved process is then monitored over a pre-determined period of time to verify improvements and performance. The final step is to create and establish a monitoring or control system that is then handed off to the process owner to assist in sustaining and maintaining the new, improved process. The objective of the control phase is to ensure that the improved process can now deliver the key variables to the process and stay within control limits, known as the specification range. The process specification range is defined by the established upper and lower specification limits or USL and LSL.
