**Percent Available** Enter the percentage of time the resource is to be available for use. If a percent is entered that is less than 100, interruptions will occur randomly and last for times that are also random with an average time of five minutes. Any expression excluding attributes is valid.

**Time Available** As an alternative to entering a percent availability, you may define availability in terms of **Time between interruptions** and the **Interruption time**, both of which may be defined as probability distributions or any other expression excluding attributes. Another way to look at this would be Mean Time To Failure (MTTF) and Mean Time To Repair (MTTR).

The length of time a resource is unavailable is randomly determined. But the average break in availability will be approximately 5 minutes.

A resource availability can be changed using a variable as the percentage, in the availability tab of the properties dialog. The following rules apply, assuming there is at least one change during simulation. 1. No value can be greater than 99%. Example: 100 & 10 will not work. 2. One of the values has to be less than 90%. Example: 99 & 89. 3. If one of the values is greater than 90% the other value can not be less than 10% of the first value. Example: 99 & 9. 4. Both values can be less than 90%. Example: 50 & 80.