Mga sumpay ha gawasIgliwat
|An Wikimedia Commons mayda media nga nahahanungod han: Segundo|
- National Physical Laboratory: Trapped ion optical frequency standards Archived 2009-02-14 at the Wayback Machine.
- High-accuracy strontium ion optical clock; National Physical Laboratory (2005)
- National Research Council of Canada: Optical frequency standard based on a single trapped ion Archived 2008-03-14 at the Wayback Machine.
- NIST: Definition of the second; notice the cesium atom must be in its ground state at 0 K
- Official BIPM definition of the second
- The leap second: its history and possible future
- What is a Cesium atom clock? Archived 2009-02-20 at the Wayback Machine.