mass resolving power in mass spectrometry

Commonly and also acceptably defined in terms of the overlap (or 'valley') between two peaks. Thus for two peaks of equal height, masses $m 1$ and $m 2$ , when there is overlap between the two peaks to a stated percentage of either peak height (10% is recommended), then the resolving power is defined as $m 1 m 1 − m 2$ . The percentage overlap (or 'valley') concerned must always be stated.

Source:

PAC, 1978, 50, 65 (Recommendations for symbolism and nomenclature for mass spectroscopy) on page 72