Four Ms

The variables that a production system manipulates to produce value for customers. The first three are resources, the fourth is the way the resources are used.

In a lean system, the Four Ms mean:

1. Material—no defects or shortages.
2. Machine—no breakdowns, defects, or unplanned stoppages.
3. Man—good work habits, necessary skills, punctuality, and no unscheduled absenteeism.
4. Method—standardized processes, maintenance, and management.