Dead-beat seconds
Looks like quartz; is considerably harder than the sweep it replaces
What it is
A mechanical watch whose seconds hand advances in one clean step per second instead of sweeping in five to ten small steps. Also called true-beat, jumping seconds or seconde morte. It looks like a quartz watch, which is the joke of the thing, and mechanically it is considerably harder than the sweep it replaces.
History
Dead seconds began in pocket watches as a reading aid: a hand that stops exactly on a marker is easier to read to the second than one in continuous motion. Jean Romilly, a Geneva-born horologist working in Paris, is credited with a dead-seconds watch in 1754, though it worked by stopping the whole movement. Jean-Moise Pouzait produced an independent dead-seconds watch in 1776 using two separate gear trains. The complication reached wristwatches properly in the 1950s and 1960s, notably through calibres from the Chezard manufacture. Rolex's own attempt, the Tru-Beat reference 6556 of 1954 with calibre 1040, was aimed at doctors taking pulse readings and sold badly enough that production stopped after about five years; surviving examples often have had the dead-seconds calibre swapped out. Quartz then made a ticking hand worthless as a novelty, and the complication went quiet until modern independents revived it.
How it works
The point to understand is that a sweeping hand is free. It is simply the escape wheel's own stepping, five to ten times a second, shown on a hand. To make a hand jump once per second you must accumulate energy for a whole second and release it in one go, which needs added parts and takes torque from the same mainspring. There are two families. The escapement-referenced approach takes its signal from the going train: Jaeger-LeCoultre's calibre 770 uses a star wheel on the escape-wheel axis with a spring arm that rides its edge and slips onto the next arm after six beats. The independent approach gives the seconds hand its own gear train and power source, as in Gronefeld's One Hertz calibre G-02, where a separate barrel drives a dedicated dead-seconds escape wheel locked and released by a lever, so the seconds indication cannot rob the timekeeping train at all.
Parts required
Either a star wheel on the escape-wheel arbor with a sprung release lever, a dead-seconds wheel and its own jumper; or, in the independent version, a second barrel, a second gear train, a dedicated escape wheel and a locking lever running in parallel with the going train.
What makes it difficult
Both families are relatives of the remontoire, and both cost amplitude, power reserve, parts count and service complexity to produce a display that a two-dollar quartz movement gives away for nothing.
In the catalog
Related
- Escapement: The mechanism that divides time into equal steps
- Tourbillon: A rotating cage that carries the entire escapement
- Small seconds: A layout that follows from how the movement is built, not an added complication