Commonly and also acceptably defined in terms of the overlap (or '
valley') between two peaks. Thus for two peaks of equal height, masses

and

,
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

.
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
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.