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.