# Preventative Maintenance Tasks Usage Trigger Calculation

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## Requirements

1. Average daily usage cannot be null.
2. Usage cannot be null.
3. Assigned preventative maintenance plan has a trigger defined for usage.

## Calculation Flow

1. Determine the frequency in days for the maintenance activity by dividing the usage from the trigger by the average daily usage of the asset.
2. Add the frequency to the last date the maintenance task was performed to determine the projected due date. If this activity was never performed before, the entry date of the asset will be used instead.

## Example

1. Equipment 9974 was entered into Cartegraph on 1/1/2014.
2. Equipment 9974's oil change plan is to be triggered every 3000 miles.
3. After several fuel log entries and heavy use, the system calculates equipment 9974's average daily usage to be 100 miles/day.
4. The frequency for oil change is determined by taking the 3000 miles from the plan and dividing it by equipment 9974's average daily usage of 100 miles/day.
3000 / 100 = 30 days
5. Since an oil change has not been performed, equipment 9974's entry date is used to determine the projected due date of the oil change.
1/1/2014 + 30 days = 1/31/2014
6. The city then performs the oil change on 1/31/2014.
7. After several more fuel log entries with lighter use, the average daily usage for equipment 9974 is found to be 20 miles/day.
8. The frequency for oil change is determined by taking the 3000 miles from the plan and dividing it by equipment 9974's average daily usage of 20 miles/day.
3000 / 20 = 150 days
9. Since an oil change was last performed on 1/31/2014, use this date to project the next due date.
1/31/2014 + 150 days  = 6/30/2014