Do you have any links to the Hargreaves papers you refer too?
The MAJOR reasons I bought an OpenSprinkler are the option to use my own WU weather station for input with the Zimmerman Method, the web interface, and the security of NOT having a device depending on the cloud like the Rachio and Blossom controllers.
I assumed the Zimmerman method was based on scientific study of irrigation using past and present weather data. I sure would like to know what Richard Zimmerman based his code on.
Don’t get me wrong, OpenSprinkler is wonderful and I wouldn’t trade it for anything. I just want to know more about the Zimmerman Method.