The Hunter ET Sensor is designed specifically for use with IMMS central control systems, exclusively with ACC controllers. ET Sensor uses solar radiation, air temperature, relative humidity, and wind (either average, or actual with the optional ET Wind sensor) to calculate evapotranspiration and communicate it to the central software via the host controller's communication. Hunter's IMMS-ET software calculates new application amounts and run times for each station, and downloads them back to all ACC controllers. ET Sensor also measures actual rainfall, which is applied to the soil reservoir before new application amounts are calculated. One ET Sensor per micro-climate is all that is needed and recommended, with a virtually unlimited number possible per central control system.