Date & Day-Date

The humble date window is the most common complication in all of watchmaking — and, surprisingly, the one most likely to get a new owner into trouble. Time to learn the one rule every mechanical-watch owner must know.

How the date works

Under the dial sits a ring with 31 printed numbers. Once a day, a finger on the movement's hour wheel catches the ring's teeth and clicks it forward one step. On cheaper movements the flip is a slow creep over the last hour before midnight; on nicer ones a spring snaps it over almost instantly at 12:00.

The one rule: respect the danger zone

Most watches let you quickset the date — crown at the first click, spin the date directly. But between roughly 9pm and 3am the date-change gearing is already meshed, and quicksetting can shear its teeth. The safe habit: pull the crown all the way out, wind the hands forward to around 6:30, then quickset freely.

Day-date and its bigger siblings

• Date — just the number, usually at 3 o'clock.
• Day-date — adds the weekday, classically spelled out at 12 (the “President” layout Rolex made famous).
• Annual calendar — knows 30- from 31-day months; needs one correction a year (March 1st).
• Perpetual calendar — knows leap years too; correct in theory until the year 2100.