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The Encyclopedia of Horology

Component record · Keyless work

Date Jumper

Partially verified

A sprung lever positioning and holding the date ring.

What it does

Snaps the date into alignment and prevents it drifting.

How it works

A finger on the driving wheel advances the ring; the jumper then drops into the next tooth to locate it precisely.

Evolution

Instantaneous and semi-instantaneous variants developed for crisper changeover.

Known variations

  • Gradual change
  • Instantaneous change

Identification for collectors

  • A date that changes slowly or sits between positions points to jumper or spring problems.

Common failure modes

  • Broken jumper spring
  • Worn jumper tip

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., Practical Watch Repairing
  2. de Carle, D., Watch and Clock Encyclopedia
  3. Daniels, G., Watchmaking

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