  The dependence of microlensing time scale frequency distributions and optical
depth toward the galactic center on galactic model parameters is explored in
detail for a distribution of stars consisting of the Zhao (1996) bar and
nucleus and the Bahcall and Soneira (1980) double exponential disk. The high
sensitivity of these two microlensing measures to the circular velocity model,
velocity dispersions, bulge mass, direction of the line of sight, bar axis
orientation, star spatial distribution and the stellar mass function means no
single galaxy property can be constrained very well without constraining most
of the others. The model time scale frequency distributions are compared with
that determined empirically by the MACHO group throughout. Although the MACHO
empirical data are matched quite well with a nominal velocity model and with a
mass function only of hydrogen burning stars that varies as m^{-2.2} to
m^{-2.5} in the M star region, uncertainties in galactic structure, kinematics
and content together with the paucity of published microlensing data preclude
any claim of the model representing the real world. A variation of the mass
function \sim m^{-1} in the M star region obtained from recent star counts,
both local and in the galactic bulge, fails to yield a sufficient number of
short time scale events compared to the MACHO data. The high sensitivity of the
microlensing measures to the direction of the line of sight may mean that
sufficient microlensing data is already in hand to constrain the bar
distribution of stars. The procedure developed here for determining the time
scale frequency distribution is particularly convenient for rapidly
incorporating model changes as data from all sources continues to accumulate.
