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| | CESIUM ATOMIC CLOCKS |
 | | Between 1953 and 1955, L. Essen and J.V.L. Parry of the National Physical Laboratory (NPL) in Teddington, England built a cesium atomic clock. |
 | | Examples are the NIST-7 standard at the National Institute of Standards and Technology (NIST) in Boulder, CO and the atomic fountains at NIST, Physikalisch-Technische Bundesanstalt (PTB), Germany, the Paris Observatory, France, and USNO. |
 | | Cesium clocks are of two general kinds: a "laboratory (or primary) standard" about as large as a railroad flatcar and a "commercial (or secondary) standard" about as large as a suitcase. |
| tycho.usno.navy.mil /cesium.html (1207 words) |
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