The Real-Time Heat Flux Extension contains two temperature, pressure and a combined temperature and humidity sensors. This extension allows an SLS system to make accurate calculation of CT2 and sensible heat flux for all - unstable and stable - conditions. 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.