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The Encyclopedia of Horology

Component record · Train

Heart Cam

Partially verified

A heart-shaped cam on a chronograph counter arbor.

What it does

Converts the hammer's blow into rotation to an exact zero position.

How it works

The hammer face slides down the cam's profile, rotating the arbor until the flat rests squarely against the hammer.

Evolution

A defining element of mechanical chronograph reset.

Known variations

  • Seconds heart cam
  • Minute-counter heart cam

Identification for collectors

  • Marks on the cam flank indicate long service or a mis-set hammer.

Common failure modes

  • Chipped cam point
  • Wear preventing accurate zero

Related photographs

Large Silver Swiss Centre Seconds Chronograph – 1894
Large Silver Swiss Centre Seconds Chronograph – 1894 — WatchMuseum.org, © WatchMuseum.org, used with permission. WatchMuseum.org catalogue record
Large Silver Swiss Centre Seconds Chronograph – 1894
Large Silver Swiss Centre Seconds Chronograph – 1894 — WatchMuseum.org, © WatchMuseum.org, used with permission. WatchMuseum.org catalogue record
Large Silver Swiss Centre Seconds Chronograph – 1894
Large Silver Swiss Centre Seconds Chronograph – 1894 — WatchMuseum.org, © WatchMuseum.org, used with permission. WatchMuseum.org catalogue record

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. 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.