1. A method for processing spectra, the method comprising: (a) obtaining a plurality of spectra, each spectrum in the plurality of spectra comprising a signal including a signal strength as a function of time-of-flight, mass-to-charge ratio, or a value derived from time-of-flight or mass-to-charge ratio; and (b) forming a signal cluster by clustering signals from the plurality of spectra with time-of-flights, mass-to-charge ratios, or values derived from time-of-flights or mass-to-charge ratios that are within a window that is defined using an expected signal width value.