Abstract: A cytometer system is described in which a stream containing sample particles flows past a light beam. The particles either naturally fluoresce or are tagged to fluoresce when they pass through the beam. The particles also scatter the light. Detectors receive the emitted fluorescent light and the scattered light and generate output signals. The output signals are processed by a configured processor to provide a signal value for later analysis of sample. In later analysis, only output signals generated by emitted or scattered light having an amplitude greater than the signal value provide an output signal.