There are many maintenance indices of which some are considered here:

• The first is Maintenance Man Minutes (MMM), how many maintenance man minutes are spent per Operational Hour (MMM/OH).
• The other index is the cost involved in maintenance per operating hour of the machine. Here the denominator term is "total operating hours". Numerator is maintenance cost for that many operating hours. The supporting costs mentioned in the numerator will involve training cost of maintenance personnel, spares, labour, utilities, equipment etc.
• Another maintenance index will be mean time between maintenance actions (MTBM). How much is the time taken for maintenance of the equipment on an average basis? MTBM is a very useful and popular index.
• Lastly, we also have the Achieved Availability AA this means how much is the equipment really utilised in a given situation keeping aside all theories!