Besides visual artistry, the tourbillon was also conceived for timekeeping precision. Nevertheless, running on time is but part of the equation; to be as uncompromisingly accurate as possible, one should also be able to set a tourbillon wristwatch with great precision, as a first step towards minimising timing errors. A Lange & Sohne studied this issue, and its answer is the 1815 Tourbillon featuring hacking seconds and zero-reset.
The hacking seconds function stems from the need to be precise. Like most things in watchmaking, really. If you need to set your watch, most of the time you pull out the crown, mess around with the position of the hour and minute hands, and then you’re all set. That’s the general idea. However, you’ll have noticed that the watch movement doesn’t actually stop running at any point. Pulling out the crown just disengages the motion works from the rest of its mechanical buddies.
The hour and minute hands are depowered, but you can see the balance wheel still whizzing away like mad, and the seconds hand is usually still running. So even if you can set the hours and minutes with pinpoint accuracy, the seconds hand is still gonna be doing its own thing. And if you’re the kind of watch lover who prizes accurate time indication down to the very second (which is a substantial percentage of watch lovers, let’s admit it), then this is going to have you reaching for the Xanax.
A watch with a hacking seconds function stops the movement entirely, making it easier to synchronise your watch against any given timekeeper. A little brake lever shows up when you pull out the crown, and presses lightly against the balance wheel, stopping it from oscillating. Stopping everything in the movement, really, since everything is controlled by the balance wheel. It’s not called the heart of the watch for nothing, you know.
The next level up from the hacking seconds is the seconds zero-reset. So, in addition to the balance wheel brake, you have an extra little heart cam sitting on the wheel that drives the seconds hand. Pulling out the crown causes the brake to press against the balance wheel and also causes a sprung hammer to fall onto the eccentric heart cam, bringing the seconds hand back to the zero position.
Strictly speaking, you can set your watch equally precisely wherever your seconds hand has stopped. It’s just neater to do it with a zero-reset, so why would you prefer otherwise? It’d be like starting your rental lease on the 9th or setting your daily alarm for 7:42am; I mean you could do it, it’s a free world after all, but who actually does that if they have a choice? Psychopaths, that’s who. Nobody sane, is what I mean.
Now we come to the good stuff. How does one combine the precision setting of a zero-reset hacking seconds with the precision timekeeping of a tourbillon? Braking a balance wheel is straightforward enough, but when said balance wheel is surrounded by a rotating tourbillon cage, how do you get to it without having your brake lever occasionally crash into the tourbillon cage instead of meeting its intended target? Bad news: it’s not easy. Good news: someone else already did it.
Back in 1997, A. Lange & Söhne’s release of the Sax-0-Mat symbolised the German company’s dedication to the principles of precision timekeeping. Fun fact: most people pronounce it “sax-oh-mat”, but what is often mistaken for a letter O is actually the numeral 0, acknowledging the movement’s zero-reset function. It was only natural that they would extend these standards for precision setting to their beautiful tourbillon timepieces as well.
The solution that A. Lange & Söhne came up with for the 1815 Tourbillon was both simple and direct, a consequence of their Teutonic fondness for efficient engineering, perhaps. Instead of a thin blade spring of limited geometry acting as a brake, the A. Lange & Söhne formulated a special spring that has to be bent by hand to conform to a very particular shape so that successful braking of the balance wheel is achieved no matter where the arms of the tourbillon cage are.
The result is, of course, spectacularly beautiful yet sensible watchmaking, which is defines the world of Lange watch collecting.