  The only allowed source of the gravitational field in the unimodular theory,
invariant under area-preserving (transverse) diffeomorphisms as well as Weyl
transformations, is just the traceless piece of the energy-momentum tensor.
This fact notwithstanding, the free energy produced by arbitrary sources (not
only static ones) is identical to the one predicted by general relativity. This
encompasses all weak field tests of gravitation.
