We develope a relativeistic theory of clock syncronization that does
not use or depend on a Newtonian framework or real time. Within the
context of this theory, we focus on the problem of estimating the
time on a remote clock.
The concept of {\it rapport\/} is generalized to capture the situation
when such an estimate is sufficient for clock syncronization purposes.
With a single property, called the {\it Observable Drift Property}, we
can characterize the information flow required for obtaining rapport.
We compare our relativized and observable concepts with analogues based
on the notion of real time in order to show that we are studying the
right quantities.
(Joint work with D. Dolev and R. Strong)