  We discuss the definitions of standard clocks in theories of gravitation.
These definitions are motivated by the invariance of actions under different
gauge symmetries. We contrast the definition of a standard Weyl clock with that
of a clock in general relativity and argue that the historical criticisms of
theories based on non-metric compatible connections by Einstein, Pauli and
others must be considered in the context of Weyl's original gauge symmetry. We
argue that standard Einsteinian clocks can be defined in non-Riemannian
theories of gravitation by adopting the Weyl group as a local gauge symmetry
that {\it preserves the metric} and discuss the hypothesis that atomic clocks
may be adopted to measure proper time in the presence of non-Riemannian
gravitational fields. These ideas are illustrated in terms of a recently
developed model of gravitation based on a non-Riemannian space-time geometry.
