https://doi.org/10.1351/goldbook.R05321
The ability to distinguish between ions differing in the quotient mass/charge by a small increment. It may be characterized by giving the peak width, measured in mass units, expressed as a function of mass, for at least two points on the peak, specifically at fifty @P04483@ and at five @P04483@ of the maximum peak height.
Sources:
Orange Book, 2nd ed., p. 203 [Terms] [Book]
PAC, 1978, 50, 65. (Recommendations for Symbolism and Nomenclature for Mass Spectroscopy) on page 72 [Terms] [Paper]
PAC, 1991, 63, 1541. (Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)) on page 1554 [Terms] [Paper]