HP Data Explorer 4 Series - Manual (Page 394)

Appendix B Overview of Isotopes
B-6 Applied Biosystems
B
B.2 Monoisotopic
and Average Masses
When isotopes are clearly resolved (Figure B-6), the
monoisotopic mass is used for mass labeling, and
corresponds to the lowest mass peak in the cluster.
Figure B-6 Monoisotopic Mass
When isotopes are not resolved (Figure B-7), the average
mass is used for mass labeling, and corresponds to the
centroid of the unresolved peak cluster (weighted average of
all isotope peaks in the cluster).
Monoisotopic mass
corresponds to
lowest mass peak