  High-resolution N-body simulations are used to investigate systematic trends
in the mass profiles and total masses of clusters as derived from 3 simple
estimators: (1) the weak gravitational lensing shear field under the assumption
of an isothermal cluster potential, (2) the dynamical mass obtained from the
measured velocity dispersion under the assumption of an isothermal cluster
potential, and (3) the classical virial estimator. The clusters consist of
order 2.5e+05 particles of mass $m_p \simeq 10^{10} \Msun$, have triaxial mass
distributions, and significant substructure exists within their virial radii.
Not surprisingly, the level of agreement between the mass profiles obtained
from the various estimators and the actual mass profiles is found to be
scale-dependent.
  The virial estimator yields a good measurement of the total cluster mass,
though it is systematically underestimated by of order 10%. This result
suggests that, at least in the limit of ideal data, the virial estimator is
quite robust to deviations from pure spherical symmetry and the presence of
substructure. The dynamical mass estimate based upon a measurement of the
cluster velocity dispersion and an assumption of an isothermal potential yields
a poor measurement of the total mass. The weak lensing estimate yields a very
good measurement of the total mass, provided the mean shear used to determine
the equivalent cluster velocity dispersion is computed from an average of the
lensing signal over the entire cluster (i.e. the mean shear is computed
interior to the virial radius). [abridged]
