Automatic Seasonal Adjust allows the Rain Bird server to keep track of local weather based upon the programmed ZIP/Postal Code. The Rain Bird server will calculate a daily Evapotranspiration (ET) rate for each ZIP code and translate to an appropriate seasonal adjust value. The seasonal adjust value is then sent to each timer in that ZIP code. This is done every day to ensure the watering duration is increased or reduced as local weather changes. It is important that if you use this feature that the watering schedule is based upon the hottest/driest time of year.