For example, for the ion C7H72+ has an exact mass of 91.0 Da and a charge number of +2, the the ion will be observed at 45.5 Th in a mass spectrum.
An interesting part of their proposal allowed for negative values for negatively charged ions. For example, the benzoate anion would be observed at m/z 121, but at -121 Th since the charge number is -1.
Unfortunately, the article proposing the unit of the thomson contains an ambiguity relating to the specification of charge. In one place the article refers to "charge number," as noted above, but in another place the article specifies charge in terms of actual units of charge: "Using standard rules for abbreviation, we have 1 Th = 1 u/ atomic charge." Or in other words the units of the thomson are units of mass (unified atomic mass units) divided by units of charge (atomic or elementary charge). This unfortunate ambiguity may have contributed to the controversey over the unit. The ambiguity about specification of charge does not affect the numerical value assigned to the mass-to-charge ratio of an ion, but instead relates to the dimensionality to be associated with the quantity. Clarification of the original intent of the authors has not appeared in the literature, although in private communications Rockwood states that the intended dimensionality was mass/charge with the specific units being unified atomic mass units per elementary charge.
In his book, Mass Spectrometry Desk Reference, Sparkman argues strongly against the use of the thomson,. However, his arguments were against a dimensionless unit because of the possible confusion with the Thomson number in fluid dynamics, Thomson scattering, and the Thomson coefficient (the latter named after Lord Kelvin). He seems not to have realized that the unit "thomson" is not dimensionless but actually of dimension mass/charge and that therefore the possibility of confusion is minimal.
The thomson is not a SI unit, nor is it currently accepted by IUPAC; however, it can be argued that the thomson complies better to the international standards about quantities and units as described in ISO 31 and the IUPAC green book than the "unitless" m/z that is widely used for labeling mass spectra.