One of the nice things about hanging around the watch beat long enough is that sooner or later the sheer force of the time you’ve spent in the field makes people feel all right about inviting you to participate in things. In my case, this year I was invited to be a juror at the Grand Prix d’Horlogerie de Genève, which is a series of awards given to participating watches once per year, in Geneva (in other words, just what it says on the tin).
The jury deliberations were interesting for a number of reasons – for one thing, it was a full day of sometimes very spirited and even occasionally heated discussion of the merits of a huge range of watches, with some of the best and brightest in contemporary watchmaking. One juror this year is Philippe Dufour, and I took the opportunity during a coffee break to overcome being somewhat overawed at being a fellow juror with one of the living legends of Swiss watchmaking, and corner him and ask him something I’ve been wanting to ask for years: What’s the rationale for the Duality?
The Duality is, for many of us, a rather enigmatic watch. Dufour made very few of them; they were produced by him for a short period of time in the late 1990s; 25 had originally been planned, but only nine were eventually made. They caused a big stir in the years immediately following their release, but due to their rarity, and thanks to the fact that their owners have been reluctant to part with them, they’ve been pretty under the radar for at least the last decade, and not much has been written about them. However, at the latest Phillips auction, Duality No. 00 came up for sale and eventually sold for the quite impressive sum of $915,000, more than doubling its estimate.
The Duality is based, conceptually and mechanically, on some school watches made in the Vallée de Joux watchmaking school in the 1930s. These were double-balance pocket watches, with a single gear train and two balances. The power was delivered to each balance by a differential. For the Duality, Dufour had to shrink down the differential mechanism to something about the size of a match head. This would be quite an achievement today, but in the 1990s it was completely unprecedented.
In our brief conversation Dufour mentioned that the differential posed a bit of a headache; he said it was “very difficult” to visualize how it would work. In particular, he knew that if he stopped one balance, the other should continue to run but he wasn’t sure that would actually be the case until he had completed one of the movements. (Even now, years later, when he talks about it you can sense the pleasure and relief he must have felt at seeing it work properly). Another interesting piece of information, which I hadn’t previously been aware of, is that if you do stop one balance completely, the other will continue to run but the seconds hand will take two minutes, not one minute, to go once around the dial. This makes sense in retrospect, when you remember that the whole rationale behind the Duality is to take the average of the rate of two balances, but it certainly would never have occurred to me that this was the case if Dufour hadn’t told me.
Dufour says that the basic idea behind the Duality is, as most of us generally know, to take the average of the rate of the two balances. For this technical solution to give a better rate, he adjusted one balance to run slightly fast and the other to run slightly slow. In such a situation, across positions, rate variations would tend to cancel each other and you should get less positional variation (which results from residual errors in the poise of the balances). One point that came up in the comments when HODINKEE’s Stephen Pulvirent covered the Duality prior to the auction, was whether or not the opposed pinning points of the balance springs should also tend to cancel positional errors in the vertical positions and Dufour says that this is indeed the case, although of course the main theme is the averaging of all rates across all positions.
While none of these points were complete revelations, being able to ask Dufour directly about his views on his own creation cleared up some basic gaps in my own understanding of the watch (in a million years I’d never have thought to wonder what happens if you stop one balance completely but it turns out, the result is a fundamental expression of how the differential works) and his clarification of the adjustment process for the two balances was most valuable. The Duality is now a near-million dollar rarity, but it says something about Dufour’s ingenuity, and his candor about his own working processes, that it’s still a subject for thought-provoking discussion twenty years after its birth.