  An important figure of merit for the performance of single-molecule magnets
(SMMs) is the 100 s blocking temperature T$_{\mathrm{B}100}$. It is the
temperature at which the remanence or zero field relaxation time is 100
seconds. If there is more than one relaxation process of the magnetisation, the
determination of the relaxation times may, however, become ambiguous. Here we
propose an operational definition for the zero-field magnetic relaxation times
from which T$_{\mathrm{B}100}$ may be determined. This definition allows for a
direct comparison of the performance of different samples independent of the
details of the relaxation processes involved in the demagnetization.
