Complication · Calendar & astronomy
Simple (Date) Calendar
VerifiedA calendar mechanism showing the date (and often day and/or month) which requires manual correction at the end of short months, because it does not account for months of fewer than 31 days.
Definition
A calendar mechanism showing the date (and often day and/or month) which requires manual correction at the end of short months, because it does not account for months of fewer than 31 days.
Historical origin
Date indications appear on watches from the seventeenth century onward; the mass-produced, quick-set date wheel became a mainstream feature of wristwatches from the mid-twentieth century.
How it works
A date ring or disc, typically toothed on its inner edge, is advanced by one tooth per day via a date jumper driven from the motion work — usually a finger or cam completing one rotation every 24 hours that pushes the date ring forward at midnight.
Because the date ring simply counts to 31 before rolling over, months shorter than 31 days require the wearer to manually advance the date at month's end, which is the defining limitation of a simple as opposed to annual or perpetual calendar.
Many movements add a rapid-correction mechanism operated via the crown or a corrector pusher, engaging a separate wheel to jump the date forward without disturbing the running time.
Pocket watch context
Date-only or date-and-day calendar pocket watches were produced from the eighteenth century, often combined with moon phase in a single calendar dial layout.
Wristwatch context
Extremely common in modern mechanical and quartz wristwatches, frequently paired with a day indication in a 'day-date' layout.
Clock context
Date calendar clocks, particularly French and American mantel and wall clocks from the nineteenth century, use an equivalent disc-and-jumper mechanism driven from the clock's own 24-hour motion work.
Identification
- Date aperture or subsidiary date hand requiring manual advance after months of fewer than 31 days
- Quick-set corrector (recessed pusher or crown position) present on many but not all examples
- Midnight date change that may 'creep' over several hours on lower-grade or worn examples rather than jumping instantaneously
Servicing notes
Date-change timing and crown-position correction are common sources of user-induced damage (changing the date in the disallowed 'danger zone' around midnight can bend the jumper); repairs to the change mechanism should go to a watchmaker.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Diagram
Sources & references
- de Carle, D., Watch and Clock Encyclopedia
Where sources disagree, the disagreement is stated rather than resolved silently.