Feature: The Big Date Complication
If you’ve ever seen a movement without it’s watch, and it’s got a date, you’ll know that the display consists of a large disc with the numbers 1–31 written on it that incrementally rotates every 24 hours. Fairly simple to understand, and also a little tricky to see—hence the big date complication. But how on Earth does the big date actually work?
Despite perpetual calendars having existed for almost as long as the clock itself, the date display in isolation is something of a modern—relatively speaking—invention. The wristwatch was well on its way to quashing the pocket watch as the new favourite, thanks to the requirement for a timekeeping device that could be read hands-free during the war, and the stage was set, ready for anyone to take a chance.
And it was Rolex, a young company that had been pushing wristwatches hard since the turn of the century, that got there first. Not Patek Philippe, not Breguet—Rolex. Rolex made simple, rugged wristwatches to be worn by people in industry getting their hands dirty; a complication like a date was more the forte of one of the old masters.
But I suppose the old masters, revelling in their ability to fit a full perpetual calendar into a tiny wristwatch, didn’t even stop to think that just the date by itself might actually be quite useful. But Rolex did, and in 1945, the DateJust was unveiled, a watch not with day, month, year or leap year—just the date.
It was a hit, of course, because it meant people didn’t need to buy the newspaper anymore just to find out what the date was. And the funny thing is that, as a complication, it was so simple, such easy pickings. All that’s needed is a disk with all 31 numbers on it and a wheel coming from the drivetrain geared to turn very slowly, with standalone teeth that mesh with the disk whenever a full day is done. That, and a window to see the disk through.
On top of the water-resistant Oyster case developed a few decades prior, it was this self-changing date that really set Rolex up as a proper watchmaker, the perfect foundation to lead into the 50s and to a lot of the models that have become so globally known.
But the simplicity is not without its faults: having a single disc with all 31 numbers on it demands a very small font—but if you wanted it to be bigger, how would you get it to fit?
The Rolex way to overcome this problem was to simply stick a magnifying lens over the date, which, really, is more of a bodge than a solution in watchmaking terms. No, something more ingenious was needed, but before we can get there, we need to resolve another small issue first—the instantaneous change.
Because a date wheel is activated by a continuously—and slowly—turning gear, the engagement can’t be instantaneous. From the moment the tooth makes first contact to when it disengages usually covers about four hours, resulting in a slow change that overlaps dates in the display. Fortunately, you’d usually be asleep at this point anyway, but if you’re going to go to the effort of improving the size of the date then it makes sense to address this first.
As a lot of watchmaking tends to be, the solution is cleverly simple. What’s needed is an instant switch, and that requires the conversion of, crudely speaking, an analogue signal into a digital one, a constant motion into two static positions with an immediate transition. The solution is a toothed spring, and not much else. Its tension keeps the date wheel in place as the changing action begins, and then forces the change in one quick motion as the crest of the tooth is overcome.
All that’s left to figure out is how to fit the big numbers in a small dial. Obviously, a single disk with all the numbers wouldn’t fit, and so a different tack is required, one that was first investigated by a watchmaker called Solvil in 1932, and refined by A. Lange & Söhne with the seminal Lange 1 in 1994. Again, the solution was quite simple: each set of digits, the tens and the ones, get their own wheel.
Of course, the tens only need to cover four digits, 0, 1, 2 and 3, and so the Lange 1 balances a wheel with the ones, counting from 0 to 9, with a cross-shaped piece with four numbered tabs that tucks in close to cater for the tens.
The cleanest solution, however, is seen here in this Girard-Perregaux Vintage 1945, which overlaps two disks of the same size for a symmetrical central position. This would, ordinarily, take up too much space, but by utilising a transparent disk on the left for the ones, over an opaque disk on the right for the repeating tens—basically placing them on the opposite sides to what you’d expect—the overlap is big enough to fit them both in.
It’s taken a long while and a lot of iterations to get the big date to the refined stage it’s at now, and it’s hard to believe it’s taken this long to get there—but here it is, and it’s a pretty impressive example of creative thinking.
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