# Timestamps are not a total ordering

UTC timestamps, local time and ordering events from separate processes.

Category: RESEARCH NOTES
Canonical: https://fieldnotesarchive.org/wiki/timestamps-and-ordering

A timestamp describes a clock reading. It does not guarantee that clocks on different machines agree, or that two events with the same timestamp happened simultaneously.

```text
2026-09-04T12:30:00.000Z
```

## Keep timezone information

Use an explicit UTC offset when exchanging timestamps. Local times around daylight-saving transitions can be ambiguous or nonexistent. Preserve the original timestamp when converting data.

## Measure duration with a monotonic clock

Wall clocks can move after synchronization or manual adjustment. A monotonic clock is suitable for measuring elapsed time within a process, but readings from separate machines are not automatically comparable.

## Separate observation and occurrence

For an event stream, store the server's receipt time separately from a client-supplied occurrence time. A server-assigned sequence can order receipt without claiming to establish the true order of events across clients.