@ronjonp, sorry for the delay on getting back to you.
Efficiency, or Distribution Uniformity (DU) refers to how evenly the sprinkler system applies water to an area being irrigated. Since no irrigation system is perfect, a deduction should be applied to correct for inefficiencies, the Scheduling Multiplier (SM) is used to help estimate the additional amount of water required to achieve an acceptable appearance.
The typical practice to apply more water is to increase the run time on the controller. The SM provides guidance on how much extra time could be needed. It helps determine the upper scheduling boundary by increasing the number of minutes that sprinklers would operate to deliver an adequate amount of water. There are many other factors that influence how much extra water should be applied, including the required appearance, use of the turfgrass area, and horticultural maintenance practices. The SM also partially recognizes that there is lateral movement of water in the soil. The scheduling multiplier is based upon the following equation:
SM = 1/(0.4+(0.6*DUlq)
SM = scheduling multiplier (decimal)
DUlq = lower quarter distribution uniformity (decimal)
0.4 and 0.6 = constants
If the DUlq is below 40% (0.40), then time and effort should be spent identifying what needs to be done to assure the system is operating correctly. This may include seeking the services of a certified designer and/or contractor to identify the factors that are causing such poor performance. When the DU is low, it is hard to justify the amount of additional water needed to minimize stressed areas and achieve an acceptable appearance. When additional minutes of run time become excessive, runoff potential increases, and it becomes more difficult to do proper maintenance.
I hope this helps to address your confusion. Please let me know if you have any further questions or concerns we can address.