US Patent 7412303 Evapotranspiration unit for re-programming an irrigation controller

An evapotranspiration (ET) unit includes a first communication link, a processor and a second communication link. The first communication link receives actual ET data from a plurality of environmental sensors. The processor calculates changes to a set of watering schedules of a predetermined watering program of a separate irrigation controller based on the actual ET data. The changes can increase or decrease the frequency and/or length of ON times for selected stations. The second communication link transmits the changes to the irrigation controller.