The purpose of the visit was the comparison of global solar irradiance measurements between the spectroradiometer operated by IASB (BRU) and the travel standard B5503 within the project QASUME. The measurement site is located at Brussels; Latitude 50.796 N, Longitude 4.357 E and altitude 120 m.a.s.l. The horizon of the IASB measurement site is nearly free in direction from W to N to S. In the direction S to SW trees obscure the horizon by up to about 15°. The local environment is urban.The Royal Meteorological Institute (RMI) participated with two Brewer spectrophotometers to this intercomparison, the single monochromator Brewer#016 (KMI), and the double monochromator Brewer #178 (RMI). The instruments RMI and KMI were distant by 100 m from B5503 which might induce some uncertainties into the comparison of the instruments. The horizon of the RMI site is obscured in direction N to NW by 2 satellite antennas, up to 40°. B5503 arrived at Brussels in the afternoon of September 3, 2004. The spectroradiometer was installed in a temperature stabilized room below the measurement platform of IASB. The intercomparison between B5503 and RMI and KMI lasted 2 1/2 days, from noon of September 6 to the evening of September 8. B5503 was calibrated several times during the intercomparison period using a portable calibration system. Two lamps were used to obtain an absolute spectral calibration traceable to the primary reference held at ECUV which is traceable to PTB: T57825 (100 W) and T61251 (250 W). The responsivity of the instrument based on these calibrations varied by less than 0.5% during the intercomparison. The internal temperature of B5503 was 27.1°C and varied by less than 0.4 °C. The diffuser head was heated to a temperature of about 25±3°C. The wavelength shifts relative to an extraterrestrial spectrum as retrieved from the SHICRivm analysis were between ± 50pm in the spectral range 310 to 400 nm.