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The Encyclopedia of Horology

Complication · Display

AM/PM Indicator

Partially verified

A simple 24-hour indicator showing whether it is day or night.

Definition

A simple 24-hour indicator showing whether it is day or night.

Historical origin

Often paired with a second time zone to ensure the wearer knows if it is morning or afternoon at home.

How it works

A disc half-painted white/yellow and half-painted blue/black rotates once every 24 hours behind a window.

Pocket watch context

Found in some travel pocket watches.

Wristwatch context

Common in GMT and world-time wristwatches.

Identification

  • A sun and moon symbol or a simple bicolor disc

Servicing notes

Linked to the hour hand; must flip at noon and midnight.

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

Diagram

top plate or bridgespillar platebalance and cockwheel train between the plates
Schematic: plate and bridge layout. 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.