Determining the optimal replacement time for spares (spare parts) with an unacceptable interval, needs to account for:

Key performance indicators can be classified as leading or lagging indicators. An example of a lagging indicator for manufacturing is:

Preventive Maintenance is defined as: Maintenance tasks, including inspection, service and or replacement, conducted at regular, scheduled intervals of calendar or operating time established to avoid failure based on average statistical anticipated lifetime.
There are cautions regarding the application of PM: No more than "A" percent of total failures are time based, wear out, in nature. .... thus. PM is an ineffective avoidance action for about *'B" percent of probable failures.

The Maintainability of a machine may be measured by:

What is the importance of the P - F Curve with respect to condition monitoring?