It appears I too am experiencing problems with the Zimmerman method calculation. Here is what my weather diagnostics say:
• Min Humidity 50%
• Max Humidity 90%
• Mean Temp 61.9
• Precip yesterday 0.13″
• Precip today 0.02″
• Current % Watering 14%
–> However, if I plug these values into the equation I get -102.4 which means the value should be clamped at zero, right? Further, the % watering has not changed in several days even though previously we received no rain and the calculation yielded significantly higher numbers (like around 30).
It appears no matter what, the number is stuck at 14%. Any ideas?