With our continous developement of the silicon irradiance sensor we have improved significant the measurement uncertainty. Especially for the standard types in the Si sensors, the use of a reference sensor calibrated by the German National Metrology Institute (PTB: Physikalisch Technische Bundesanstalt) has significantly reduced measurement uncertainty. At the same time, all our sensors can benefit from optimisation to the calibration system and more accurate component specifications. From now on all Si sensors (standard types) have a measurement uncertainty of ± 5 W/sq.m ± 2.5% of measurement (previously 5% from end of measurement range). The standard types of SiS sensors are specified with ±5 W/sqm ± 3.5% from reading (until now 5% from end of measurement range). The measurement uncertainties apply throughout the whole working temperature range, for the AM1.5 spectrum and vertical light. The calculations were carried out in accordance with GUM (Guide to the Expression of Uncertainty in Measurement) where k=2 Added to this, as of now, all standard types in the Si and SIS ranges are specified for a working temperature range of -35 to +80°C.