“…In view of the fact that spread of the parameters is also a characteristic of the system the semicircular shape of the data cloud suggests the presence of additional important information -high variability in the parameters. According to [12], in fl uorescence fl uctuation spectroscopy a spherical cloud is expected for monomers, dimers, and even aggregates of a certain protein with relatively stable characteristics, while an ellipsoidal cloud is expected for a mixture of molecules of several types. In our investigation, however, elongation of the cloud may be the result of an increase in the variance of the measured parameter, indicating the formation of a certain type of aggregate or the presence of unavoidable experimental eff ects (photobleaching, uncontrolled ligandizing of monomers by nonremovable impurities, etc.…”