Complication · Display
Jump Hour
Partially verifiedA display in which the hour is shown in a numbered aperture (rather than by a conventional hand) and changes instantaneously — 'jumping' — from one hour to the next at the top of the hour, rather than creeping.
Definition
A display in which the hour is shown in a numbered aperture (rather than by a conventional hand) and changes instantaneously — 'jumping' — from one hour to the next at the top of the hour, rather than creeping.
Historical origin
Jump-hour pocket watches (sometimes called 'digital' watches in period sources) appeared in the late nineteenth century; the wristwatch jump-hour format became a recognised Art Deco-era style in the 1920s–1930s, revived periodically since.
How it works
An hour disc, printed with the twelve hour numerals around its rim, sits beneath an aperture in the dial and is advanced by exactly one-twelfth of a revolution once per hour by a jumper spring and star wheel (a 'snap-jump' mechanism), rather than rotating continuously as a geared hour hand would.
Energy for the jump is stored gradually through the hour by a spring being tensioned by the going train, then released suddenly at the top of the hour when a triggering cam or lever passes a critical point, snapping the disc forward cleanly to the next number.
Because the jump must occur reliably and cleanly regardless of how the watch is oriented or how recently it was wound, jump-hour mechanisms require carefully tuned spring tension — too weak and the jump may hesitate or fail to complete; too strong and it can rebound or over-travel.
Jumping Hour: An hour indication that changes instantaneously rather than creeping.
Energy is stored in a spring and released by a jumper once per hour, snapping a numeral disc to the next position.
Because the jump demands a burst of energy, the design must not disturb the going train's rate.
Pocket watch context
Occasionally seen as a novelty or design variant in nineteenth-century pocket watches marketed on their unconventional 'digital' hour display.
Wristwatch context
A recognisable Art Deco-era wristwatch style, and periodically revived by manufacturers for its distinctive dial aesthetic and its associated snap-jump mechanical charm.
Identification
- Hour shown in a numbered window rather than by a hand, changing instantaneously at the top of each hour
- Often paired with a jumping or wandering minute display for a fully 'digital' mechanical dial layout
- Hours read through a window rather than by a hand
- An audible click at the hour change
Servicing notes
The jumper spring's tension is specific to the calibre and disc weight; incorrect adjustment after service is a common source of hesitant or failed jumps, so this should be tuned by an experienced watchmaker.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- de Carle, D., Watch and Clock Encyclopedia
- Precise origin date of the earliest jump-hour watch not independently established from sources consulted.
- Britten, F. J., Old Clocks and Watches and Their Makers
- Horological Journal (British Horological Institute), technical articles
Where sources disagree, the disagreement is stated rather than resolved silently.