One step, once a day.

This exhibition demonstrates a conventional semi-instantaneous date indication. It is a teaching model, not a reconstruction of a particular watch.

What the model follows

A numbered ring has 31 positions. A wheel turning once every 24 hours brings a finger to the ring. The finger begins its advance; a spring-loaded jumper completes the step and keeps the next date aligned. The hour hand makes two revolutions in the same day. The dial’s date window exposes the ring itself.

What we simplify

We stretch the change from 23:15 to midnight, including a quicker final settling interval. Those timings make the action legible; they are not a specification for real watches. All parts share one simulated clock at every playback speed.

The drive finger, teeth and jumper are illustrative geometry. Their movement is prescribed, not calculated from contact forces. The reduction train feeding the daily wheel, the going train and the setting works are omitted. Lifting the dial shows the layers, not their normal operating clearance.

“Hold to turn hands” advances the lesson’s clock. It does not teach quick-date correction or how to operate a particular crown. The simple calendar repeats 1–31 and does not recognize shorter months. No annual or perpetual calendar is implied.

Sources

• Horopedia: Date indication — peripheral disc, daily drive, jumper, and semi-instantaneous versus instantaneous systems.
• Horopedia: Date / Calendar — the 24-hour period and the limits of a simple date.
• Horopedia: Simple date display — the daily wheel and its driving finger.

These sources establish the mechanical principle. They do not validate our illustrative dimensions or simulated contact geometry.

Checks

Automated checks cover one date step per day, two hour-hand turns per day, no noon change, continuity at midnight, the 31-to-1 transition, pausing and invalid clock input.