Atomic labs, observatories, and timezone bureaus keep the global clock aligned for navigation, finance, and communications.
| City | Institution | Contribution |
|---|---|---|
| Paris | Observatoire de Paris | Historical prime meridian reference and modern timescale maintainer. |
| Greenwich | Royal Observatory | Origin of GMT and maritime navigation standard. |
| Boulder | NIST | Houses atomic fountains that define the SI second. |
| Tsukuba | NICT | Supports UTC and runs frequency standards for Asia-Pacific. |
| Tokyo | National Metrology Institute | Synchronizes Japanese standard time and satellite systems. |