There are a number of different ways that mass spectrometers can separate ions of different masses. Some systems use the mass dependent deflection of a beam of analyte ions, in a magnetic or electric field, to arrange that only ions in a limited range pass through a slit to be detected. Another common method is to created a region of static and radio frequency electric fields in such a way that only a narrow range of ion masses have stable trajectories and thus can reach a detector. However, as the name implies, a time-of-flight mass analyser measures masses by recording the ion flight time.