Z-time

Z time, spoken as Zulu time, is UTC written with the suffix Z, the convention that marks a time as being on the zero-meridian standard rather than local. The Z comes from the zone-description letter system: each whole-hour zone gets a letter, and the zero zone, centered on Greenwich keeping UTC, is zone Z. A time such as 0630Z is therefore 0630 UTC, with no ambiguity about the zone. The navigator and the GMDSS use the Z suffix on distress messages, weather bulletins, navigational warnings, and log entries so that every station, whatever its local time, reads the same instant. It is the standard way to time-stamp a position report, a sight, or an ETA.