The variables that influence a production system to produce value for customers. The first three are resources; the fourth is how the resources are used.
In a Lean system, the four M's stand for:
Material - no defects or shortages.
Machine - no malfunctions, defects or unplanned interruptions.
Human - good work routines, necessary skills, punctuality and no unannounced absences.
Method - standardized processes, maintenance and management.
