I agree completely with Mr. Morehouse. Here in the central coast of California it’s a coastal desert. We do get maritime influence in the form of really cool nights (55F) but the temperature during the day will be in the 80sF right now and the wind can be howling. And it will get a lot hotter during the day by August. Some more inland valleys can see a temperature range in the summer of 40f night to 104f day in August. Right now my Zimmerman is reading about 54% and it’s just not enough water. I don’t have enough experience with this unit to know what the Zimmerman will be in August but at this rate I do know that come July-August-September I am going to have to bias the current Zimmerman recommendations.
And that gets to be a pain in the butt because it becomes the equivalent of Manual Mode, which my old controller did just fine. The weather based water control feature was why I bought Open Sprinkler.
The Zimmerman formula needs to be tweaked or perhaps a more complex formula needs to be an option. That should include wind, degree-hours and humidity. Ultimately soil moisture should be a factor, too.