The date changes at noon, or not at all

A mechanical watch has a twelve-hour dial and no concept of AM or PM. The calendar mechanism advances once per two revolutions of the hour wheel, and it has no way of checking which of those two revolutions is the night one. Whichever twelve hours you set it in, it commits to.

So a date that flips at lunchtime is not a fault report. It is the watch telling you, accurately, that you set it twelve hours out.

Fixing it, in under a minute

1. Pull the crown to the time-setting position, which stops the seconds hand on any movement with hacking.
2. Turn the hands forward through a full twelve hours, watching the date. It should change on the way past 12.
3. If the date changed, you are now in the morning: continue forward to the correct time.
4. Push the crown home and screw it down if it is a screw-down crown.

It stays fixed. There is nothing to adjust and nothing that will drift back.

The date takes an hour to change

Normal, and worth understanding because it is one of the clearest ways a specification sheet maps onto something you can watch happen.

In a dragging date, a cam on the hour wheel slowly pushes the date wheel round over a period that can start well before midnight and finish well after. In an instantaneous or semi-instantaneous date, a spring is progressively tensioned and then releases, snapping the wheel over in a fraction of a second. The second design costs more, takes more energy from the mainspring, and is one of the small, real differences you are paying for as you move up.

Neither is a fault. If your date crawls, you own a dragging date.

The date does not change at all

Work through these in order.

• Did the watch stop? If it ran down overnight, no date change happens. Wind it and reset.
• Is the date sitting between two numbers? That is a misaligned date wheel, usually from a previous change that was interrupted. On many movements it corrects itself over the next cycle. If it does not, it is a bench adjustment.
• Does the quickset work? Check the crown position: on most movements the first click out is the date and the second is the time, but plenty of calibers reverse or omit that. If the quickset moves the date, the calendar work is engaged and driven, and the fault is elsewhere.
• Did somebody set the date at midnight? The classic damage: a broken tooth on the date wheel or a bent date jumper. This needs the movement opened.

The months with thirty days

Unless your watch has an annual or perpetual calendar, you will be correcting the date by hand five times a year, at the end of every month shorter than 31 days. That is normal and is not a defect. A calendar complication exists precisely to remove that chore, and it costs what it costs because doing it mechanically is genuinely difficult.

If you rotate several watches, expect to reset the date on each one as it comes back into use. That, rather than accuracy, is the practical daily friction of owning mechanical watches, and it is the argument our comparison of quartz against automatic keeps coming back to.

What a repair costs

Realigning a date wheel is usually a small job folded into a service. Replacing a broken date wheel or jumper depends entirely on parts availability: on a common Swiss or Japanese caliber it is inexpensive, and on a brand-only movement it can require a service center visit. Expect an independent watchmaker to quote in the region of $150 to $350 for calendar work with a case reseal, before sales tax. Rates vary widely by city and by country, so treat that as indicative and get a quote.