In contrast to a normative g-value measurement, which is done under laborious conditions with fixed boundary conditions, the in-situ g-value measurement does not strive for normative measurement results, instead it represents the more realistic solar heart gain situation under operating conditions. Thus, the measurements done within this campaign are not following a normative procedure and therefore not directly comparable to normative g-values under perpendicular solar incidence. Apart from this fact, the in-situ measurement has not defined as a target to provide a normative g-value as result, instead it should represent the behaviour of the system under real conditions. The major application of the in-situ measurement will be to measure directly on installed façade for quality assurance, either old glazing’s or new installed ones. Systems to be applied can be any kind of glazing (float, low-e, sun-protecting, EC, TC), but also complex glazings with incorporated shading or daylight redirecting devices (either mounted in-between the glazing or on the outer side, not inside). The objective of the in-situ g-value measurements is to get a more representative value for the operating g-value under non-laborous conditions. By this it should be also possible to validate simulations results and to parametrize simulation models based on real monitoring input data. Furthermore, it might be possible to provide validated measurement data for simulation models as input.