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The Encyclopedia of Horology

Clock type · Precision

Atomic Time Standards

Partially verified

Timekeeping standards using an atomic transition frequency as the reference.

Movement & mechanism

  • A microwave signal is locked to an atomic resonance, giving a highly reproducible frequency
  • The second has been defined in terms of a caesium transition since 1967
  • National laboratories compare standards to maintain international time scales

Identification

  • Laboratory apparatus rather than a clock in the furniture sense
  • Displays are derived signals, not the standard itself

Terminology

  • Caesium standard
  • SI second
  • Coordinated Universal Time

Known variations

  • Caesium beam, hydrogen maser and optical standards

Collecting notes

Originality decides value and interest: check that movement, dial and case belong together, and prefer honest wear over refinishing. Movement work belongs with a clockmaker; cleaning a dial or case yourself commonly destroys the evidence that dates the clock.

Diagram

date ring, thirty-one positionsdate aperturedriving wheel and jumper
Schematic: calendar work under the dial. An outline schematic drawn to show the arrangement of the parts discussed here. It is not a dimensioned working drawing and does not depict a particular maker's calibre.

Sources & references

  1. Britten, F. J., Old Clocks and Watches and Their Makers
  2. Loomes, B., reference works on British clockmakers (edition-dependent)
  3. Museum catalogue descriptions of comparable examples

Where sources disagree, the disagreement is stated rather than resolved silently.