  An exact nonlinear scaling transformation is presented for the local
three-dimensional dynamical equations of motion for differentially rotating
disks. The result is relevant to arguments that have been put forth claiming
that numerical simulations lack the necessary numerical resolution to resolve
nonlinear instabilities that are supposedly present. We show here that any time
dependent velocity field satisfying the local equations of motion and existing
on small length scales, has an exact rescaled counterpart that exists on
arbitrarily larger scales as well. Large scale flows serve as a microscope to
view small scale behavior. The absence of any large scale instabilities in
local numerical simulations of Keplerian disks suggests that the equations in
this form have no instabilities at any scale, and that finite Reynolds number
suppression is not the reason for the exhibited stable behavior. While this
argument does not rule out the possibility of global hydrodynamical
instability, it does imply that differential rotation {\em per se} is not
unstable in a manner analogous to shear layers or high Reynolds number
Poiseuille flow. Analogies between the stability behavior of accretion disks
and these flows are specious.
