[en] In this work measurements of random-incidence scattering coefficients in three laboratories are compared. The sample geometry is sinusoidal. These surfaces are geometrically identical, but they were constructed in different scales. So far, measurements of this kind were performed only in scale models. Using turntables in real sample size was hardly considered possible. One result of general importance is that measurements are indeed possible in real-scale reverberation rooms with turntables of 3 m diameter. There are only small differences between the real-scale and model-scale results. Some variations of the standard procedure were tested and the uncertainties identified: mounting of the sample, connection or sealing between sample and base plate, way of rotating the sample, air absorption and time variances. The results presented can be regarded as guidelines for application of ISO/DIS 17497-1.