NR01 is a market leading 4-component net radiometer, mostly used in scientific-grade energy balance and surface flux studies. It offers 4 separate measurements of global and reflected solar and downwelling and upwelling longwave radiation, using 2 sensors facing up and 2 facing down. NR01 owes its popularity to its excellent price / performance ratio and major improvements relative to comparable instruments. Advantages include its modular design with 2 pairs of identical sensors, low weight, ease of levelling, and low solar offsets in the longwave measurement. The unique capability to heat the pyrgeometers reduces measurement errors caused by dew deposition.