Statistical process control (SPC) is a tool to distinguish between "normal" and "special" cause variation. It has many applications; one of them is preventive maintenance. Equipment wear will gradually increase variation.
By identifying the normal variation of a process, you can react to special variation caused by wear of equipment. This way you can work more preventive rather than firefighting. Alarms related to the variation of your measurement (Range or stdev) can alert you when you need to replace parts.
An example is replacement of an O-ring used to test capillaries at a company. When an O-ring starts to wear, it results in greater variation in the measurements. This means it is time for maintenance. Need for cleaning can also cause increased variation. Operators with SPC knowledge can identify measurements that can predict maintenance need. Lean Tech provide SPC training and consulting.