The scheduling method sets the the new Next Due Date after a PM Master has generated a new work order.
Last Due will set the next due date based solely on the frequency count, either in days or months. The completion of the latest work order does not factor into determining when the next work order should be generated
Example: A weekly PM has a schedule method of last due and frequency of 7 days. This PM Master will generate a work order every 7 days.
Last Preformed will set the next due date based on the frequency but only once the latest work order is completed or canceled. The status of the latest work order does become a factor.
Example: A weekly PM has a schedule method of last preformed and a frequency of 7 days. The latest work order is scheduled for June 7th but is completed on June 10th. The next due date is now June 17th rather than June 14th.
Note: Last Preformed does help to lessen the possibility of having duplicate works orders generated if the completion of the PM is delayed but there is the risk that a new work order will be generated far outside of the required frequency for the PM.