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The Encyclopedia of Horology

Clock type · Specialist

Perpetual Calendar Clocks

Partially verified

Clocks that automatically account for the varying lengths of months and leap years.

Movement & mechanism

  • Complex calendar train with a 48-month wheel or similar program disc
  • Indicates day, date, month, and usually moon phase
  • High-grade movements due to the torque required to flip indicators

Identification

  • Indication of February 29th in leap years
  • Multiple calendar dials or apertures
  • Often combined with astronomical functions

Terminology

  • Perpetual calendar
  • Leap year
  • Moon phase

Known variations

  • French mantel and English longcase versions

Collecting notes

Condition and originality are paramount. For technical clocks like regulators or atmospheric clocks, the completeness of the original mechanism is more important than case condition. For decorative clocks (Boulle, Empire), the quality of the case craft is central.

Related photographs

The Prague Astronomical Clock in Old Town - 8559
The Prague Astronomical Clock in Old Town - 8559 — Jorge Royan, CC BY-SA 3.0. Wikimedia Commons file page
Czech-2013-Prague-Astronomical clock face
Czech-2013-Prague-Astronomical clock face — Godot13, CC BY-SA 4.0. Wikimedia Commons file page

No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.

Sources & references

  1. Britten, F. J., Old Clocks and Watches and Their Makers
  2. Loomes, B., The Early Clockmakers of Great Britain
  3. Roberts, D., British Skeleton Clocks
  4. Museum catalogue records

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