Universal Concord Standard Date (UCSD)

Universal Concord Standard Date (UCSD) is the civil dating standard of the Solar System Concord — the shared spine that dates in the public record convert to, whatever notation they were first written in.

The count is continuous with old Earth's common-era civil calendar — no reset, one number line — renumbered by a fixed offset: UCSD year = CE year + 200. Converting is arithmetic, not a conversion table: a document that says 2140 CE files as 2340 UCSD and nothing more is required, and the count's zero point is given no in-world significance. The standard was adopted and named within the Concord's framework and applied retroactively to earlier dates, the way calendar reforms always are — the label is newer than most of the years it labels. How the count is actually kept — the unit, the ensemble of clocks, the loop-closing — is its own article: Count and Calibration.

Three things UCSD is not:

• It is not the timeline. There is one shared history; UCSD is one notation for it. Other civilisations keep their own reckonings for the same events — a source dating an event in its own calendar names the same moment a UCSD date names, and converting between notations is bookkeeping, not cosmology. An archive's conversion tables are craft, maintained the way any reference work is maintained.

• It is not instantaneous. There is no faster-than-light communication, so time, like every other kind of information, is carried: reference clocks are compared by physical transit, calibration certificates travel with courier runs, and a distant institution's clock is only ever as current as its last synchronisation. Distant records are transit-lagged, and their dates inherit the lag.

• It is not perfectly uniform. Relativistic time dilation between regions moving and sitting differently is real physics, and far-separated records accumulate small, predicted offsets. At the scales civil record-keeping cares about the effect is minimal: reconciliation applies the known corrections as a matter of routine, files the adjustment, and moves on. The whole point of making the corrections routine is that a discrepancy which survives them has earned an instrument's attention rather than a bookkeeper's.

• The year turns at midwinter. Early Winter and Deep Winter close a UCSD year and Late Winter opens the next, so 2831 UCSD, Deep Winter is followed by 2832 UCSD, Late Winter and then by Early Spring. A stamp that reads Early Winter belongs to the year whose autumn it follows.

Example: a field log written aboard a vessel dates itself by the ship's own clock; the archive that receives it files it in the author's notation with the UCSD conversion noted beside — the original is the document, the conversion is the courtesy.