A method and a device for determining a trigger condition for presenting a registered signal on a display of an oscilloscope on the basis of a rare signal event in the registered signal. The method and device determines a level-based and/or time-based distribution of frequencies of occurrence from level-based and/or time-based parameters determined from sampled values of the registered signal in a specified corresponding level-raster and/or time raster, and compares the determined level-based and/or time-based distribution of frequencies of occurrence with a previously given corresponding level-based and/or time-based reference-distribution of frequencies of occurrence. A first trigger condition is determined dependent upon an identified difference between corresponding level-based and/or time-based distribution of frequencies of occurrence and corresponding level-based and/or time-based reference-distribution of frequencies of occurrence. A trigger signal is activated if the trigger condition in the registered signal has been overstepped or undercut.