Just because it rains doesn’t mean it necessarily stops watering. Zimmerman algorithm uses all of temperature, humidity, and precipitation to decide the watering percentage. There are a few things you want to check first:
1. Are your sprinkler programs set to ‘Use Weather Adjustment’? Watering percentage only affects programs that are set to ‘Use Weather Adjustment’.
2. Have you modified the Adjustment Method Options, such as the baseline values or weights for temperature, humidity, precipitation? These baseline values can affect how the result is calculated.
3. You can check the actual data used for calculation by going to:
where long,lat is your location’s longitude,latitude (for example: http://weather.opensprinkler.com/weather1.py?loc=42,-72.5)
this will return the percentage (scale) with raw data appended at the end.