摘要：In the statistical standard literature the stationarity of a time dependent process generally is defined by the invariance in time of the distr.bution of the variable, like a SPL （sound pressure level） fluctuating in time. However in reality there cannot exist constant distr.bution, respectively characteristics, in time in the str.ct mathematical sense because the time intervals of observation only can be finite due to practical reasons. Hence on every distr.bution and characteristics based on it a certain, but evaluable uncertainty is imposed. For monitoring these uncertainties the online-measurement technique, i.e. primarily appropriate software, is already available, also for customers. According to this state of the art the following expanded definition of the stationarity is proposed： Stationarity during a quality controlled measurement process becomes established, when the upper confidence limit of the interesting specific characteristic has no positive slope in time and correspondingly the lower confidence limit of the specific characteristic no negative slope and, as a third, a common condition, the interesting specific characteristic has adjusted itself to a constant position in time. From this a systematic criteria scheme is established and in examples applied on different in- and outdoor situations of sound impact.