The Zimmerman calculation is not working correctly, as evidenced that it changes throughout the day. Properly calculated, Zimmerman is based on the previous day’s average temperature and average humidity and the previous day’s total precipitation plus any rain today. If there’s no rain today, then the water level percentage should not change from midnight to 11:59 p.m. But it does, and it’s useless in a climate where night time temps drop significantly. There is no way that the current weather data source can work unless OpenSprinkler aggregates the hourly data calls and then computes the averages.