  In 1977, Malament proved a certain uniqueness theorem about standard
synchrony, also known as Poincar\'e-Einstein simultaneity, which has generated
many commentaries over the years, some of them contradictory. We think that the
situation called for some cleaning up. After reviewing and discussing some of
the literature involved, we prove two results which, hopefully, will help
clarifying this debate by filling the gap between the uniquess of Malament's
theorem, which allows the observer to use very few tools, and the complete
arbitrariness of a time coordinate in full-fledged Relativity theory. In the
spirit of Malament's theorem, and in opposition to most of its commentators, we
emphasize explicit definability of simultaneity relations, and give only
constructive proofs. We also explore what happens when we reduce to "purely
local" data with respect to an observer.
