Following the information above, I have deleted the WU key in order to use the OWM data for the Zimmerman weather algorithm. For the time being we have had a sunny day and the water level was hourly updated to 72% during the day. I think the weather algorithm is working in some way, but I still can’t see if there is any precipitation value from yesterday’s rainfall measurement included. It is strange that there is no possibility to see the weather data used for the Zimmerman calculation anymore. I always get the message that an API key will be needed, if I click on the Weather Diagnostics button. There is also no weather logo visible at the App’s front page. Is this a general OpenSprinkler firmware or app issue, if the Zimmerman weather algorithm is based on OWM?
It would be also nice to have some information about the weather station providing the data. We have some afternoon thunderstorm at the moment and they are very local to our area. This means their might be a heavy rainfall a few kilometers away but no rainfall at all at my home location.
I like the idea of having at least the output of the Netatmo rain gauge included in the weather algorithm. There exists the possibility to set the Open Sprinkler rain delay time by API commands forwarded from IFTTT and apilio.io applets. However a direct interface to Netatmo might be the better solution. I also bought Netatmo and OpenSprinkler as these combination seems to be perfect for garden watering. The bad news is that it relies on WU, which seems to be not working anymore.