The DEVIreg™ 850 version IV is an advanced thermostat with LED display used for outdoor ground or roof applications. The sensors provide information about both moisture level and temperature, resulting in an optimal control of the heating system. The DEVIreg™ 850 IV can handle up to 2 independent areas, in any of the following combinations: Single system for roof or ground (1 system, 1–4 sensors). Combination system: 1 ground system and 1 roof system (2 systems, 2–4 sensors total, min. 1 sensor per system); Dual system: either 2 roof systems or 2 ground systems (2 systems, 2–4 sensors total, min. 1 sensor per system). In the dual / combination systems it is possible to prioritize between the zones, e.g. if only a limited power output is available.