The Real-Time Evapotranspiration Extension contains net radiation, two soil heat flux, precipitation, two temperature, pressure and a combined temperature and humidity sensors for determining the evapotranspiration in terms of latent heat through the so-called energy-balance method. This extension also comprises all features of the Real-Time Heat Flux Extension. The sensors are sampled by a datalogger that is installed directly at the mast. From the datalogger the sensor values are digitally transmitted to the Scintillometer Processing Unit via a serial cable. The full-featured datalogger permits the user to upgrade or add additional meteorological sensors at any time. Due to the digital signal transmission the mast can be installed at remote locations, if an appropriate serial data link is provided, for example by using RS485 Converters or radio modems.