Measurement stability is the change in bias over time. It represents the total variation in measurements of the same part measured over time. This variation over time is called drift.
You can use a control chart to monitor the stability of a measurement process by measuring a master or control part on the same system over time. As measurements are taken, points within the limits indicate that the process has not changed, and points outside the limits indicate that the process has changed. Knowledge of the equipment and measurement conditions help identify special causes when the system is unstable.
An engineer measures a master color sample every shift to confirm that the densitometer in is range and can effectively monitor the printing process.