Yes, it is. It uses an ‘inches per week’ approach that includes the amount of rainfall received, the amount of water a given zone can irrigate, and the run-off limit for each zone.
With that information, each day it determines the amount of water needed to keep the ‘inches per week’ of water at the specified level.
It works, but I’m not sure it is as optimal as the ET method DanTripp has been discussing. I have his simulation program and want to run it against the ‘inches per week’ approach to see if one is materially better than the another.