  Determination of the molecular Kondo temperature $T_K$ poses a challenge in
most cases when the experimental temperature cannot be tuned to a sufficient
extent. We show how this ambiguity can be resolved if additional control
parameters are present, such as magnetic field and mechanical gating. We record
the evolution of the differential conductance by lifting an individual molecule
from the metal surface with the tip of a scanning tunneling microscope. By
fitting the measured conductance spectra with the single impurity Anderson
model we are able to demonstrate that the lifting tunes the junction
continuously from the strongly correlated Kondo-singlet to the free spin $1/2$
ground state. In the crossover regime, where $T_K$ is similar to the
temperature of experiment, the fitting yields ambiguous estimates of $T_K$
varying by an order of magnitude. We show that analysis of the conductance
measured in two distinct external magnetic fields can be used to resolve this
problem.
