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The Encyclopedia of Horology

Complication · Calendar & astronomy

Leap Year Indication

Partially verified

A display showing the position of the current year in the four-year leap cycle.

Definition

A display showing the position of the current year in the four-year leap cycle.

Historical origin

A functional element of perpetual calendar work, exposed on the dial so the wearer can verify correct setting.

How it works

A four-year wheel advances once per year, driving both the February correction and the dial indication.

Because it turns once every four years, correct setting is essential and easily mistaken.

Pocket watch context

Found in the most elaborate pocket calendar watches.

Wristwatch context

Standard alongside perpetual calendar displays.

Identification

  • A subsidiary indication reading one to four, or marked for leap year

Servicing notes

This is specialist work. Levers, springs and cam profiles in complicated work are calibre-specific, and incorrect reassembly commonly damages parts that cannot be bought. Refer the movement to a watchmaker experienced with this mechanism.

General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.

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. de Carle, D., Watch and Clock Encyclopedia
  2. Britten, F. J., Old Clocks and Watches and Their Makers
  3. Horological Journal (British Horological Institute), technical articles

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