The OEE (Overall Equipment Effectiveness) Method
Applying this method has allowed us to start making close evaluations on the performance of the maintenance interventions. For this reason, the OEE index is considered the indicator for the excellence of the Toyota Production System, and is a direct expression of TPM philosophy. OEE is the result of three different levels of efficiency:

• Availability of the machine, which refers to all shutdowns that occur (breakdowns, maintenance, set-ups, adjustments);
• Performance, which refers to speed reductions in the production cycle;
• Quality losses, which refer to waste, defects, reworks.

The OEE index is normally defined by the following formula:
 
OEE = system availability level x efficiency x rate of quality
 
With the OEE method, we can accurately assess whether the maintenance interventions or inspections made to improve the performance of the machines have provided positive results. We thereby have control of the value losses (through inactivity, defectiveness, speed) which could reduce the operative availability of the machines.
By using this method we check a series of efficiency indicators which allow us to monitor system performance:

1. MTBF (mean  time between failure):
2. MTTR (mean time to restoration)
3. losses in yield at start-ups;
4. losses for stops
5. losses for set-ups
6. losses in speed
7. losses for defectiveness
8. gross available time;
9. time available for work;
10. functioning time;
11. useable operative time;
12. useful time lost.