Watches & Wonders 2026: The TAG Heuer Monaco Evergraph Introduces A New Chronograph Control System

The biggest news from TAG Heuer at Watches & Wonders 2026 is not only big for TAG, it’s pretty big news in general. The new TAG Heuer Monaco Evergraph is a Monaco-cased watch, with the left hand crown and right side pushers of the original design, 40mm across, in titanium or DLC coated titanium. It’s a sharp looking watch, but the open dial alerts you immediately to the technical innovations inside, which include the TH-Carbonspring balance, as well as the use of a chronograph switching mechanism which replaces the cam-and-lever or column wheel switching systems found in virtually all other chronographs.

On the externals, we have a classic Monaco square case, water resistant to 100 meters (water resistance in a watch with sharp case corners was a challenge for the early versions of the Monaco thanks to the difficulty of making non-round gaskets). The watches have domed sapphire crystals, and the dial itself is transparent acrylic, with hands and applied markers, both coated with Super-LumiNova. There is a center chronograph seconds hand and, at 3:00, a 30 minute chronograph register, and the black DLC coated movement bridges are visible through the dial, as is the TH-Carbonspring oscillator.

The TH-Carbonspring Oscillator

Research into carbon fiber as a material for balance springs, has historically been motivated by the search for alternatives to Nivarox type alloys and also to silicon. The earliest example of a carbon fiber balance spring I’m aware of, is the so-called Carbontime oscillator, which was developed to a prototype stage by Gideon Levingston, but which was never produced in series, or commercially. TAG Heuer introduced carbon balance springs initially in 2019, but some unsolved technical problems remained to be solved and it was not until last year that TAG Heuer released a new version of the TH-Carbonspring system, in the Monaco Flyback Chronograph TH-Carbonspring and Carrera Chronograph Tourbillon Extreme Sport TH-Carbonspring.

The TH-Carbonspring balance spring and balance, as used in the Monaco Flyback Chrongraph TH-Carbonspring; the version used in the Evergraph is freesprung, with inertial timing weights.

Carbon fiber as a material for balance springs is attractive for several reasons – it’s unaffected by magnetism, and highly shock resistant. The process for making balance springs involves growing carbon nanotubes on a wafer, and then embedding them in a carbon matrix (the nanotubes are oriented vertically with respect to the plane of the spring). The biggest problem was that the material as it was first used, tended to absorb water and also had the potential to absorb oils, which would change the performance characteristics, and this was eventually solved by giving the carbon springs a hydrophobic and oleophobic coating (that is, one that repels oils and water). The carbon balance spring is paired with a balance made of aluminum, with gold rim weights (which TAG Heuer says are there for temperature compensation, although as they’re distributed along the rim, they would also offer better angular momentum than if they were absent). TAG Heuer is running the balance at 5Hz in the Evergraph, or 36,000 vph.

The second major innovation in the Evergraph, is the so-caled bistable switching mechanism, which was designed in partnership with Vaucher Manufacture Fleurier (Vaucher, says TAG Heuer, was also its partner in designing the movements for the calibers TH81-00 and TH81-01 found in the TAG Heuer Monaco Split-Seconds Chronograph and the TAG Heuer Carrera Split-Seconds Chronograph.

The Evergraph Bistable Chronograph Switching Mechanism

The bistable switching system is visible through the back of the Evergraph, below the rotor for the automatic winding system.

Above is the chronograph switching system, along with some of the essential components of the chronograph gear train. There are three wheels visible: on the far right is the chronograph seconds wheel with its heart cam; below it and to the left is the vertical clutch; and to the far left, is the minute recorder, with its return-to-zero heart cam. The heart cams are acted on, during reset, by a single piece reset-to-zero hammer; the minute recorder is held in position by a jumper spring.

Above is the initial position of the chrongraph train, prior to starting the chronograph. The “bistable” element is in red. The term “bistable” here means that this flexible blade has one of two stable configurations: one in which its convex side is to the left, and one in which it is to the right. The reset to zero hammer is resting on the upper, flat surfaces of the reset-to-zero heart pieces, holding them in their zero position. Note that the one piece reset hammer is also a bistable component; inside it, there are two horizontal blade springs which control the position of the reset hammer’s faces with respect to the heart pieces.

Chronograph Start

When the chronograph start pusher’s pressed, the bistable blade (below, red) snaps into its other stable position. This is like a playing card or business card being snapped back and forth in your fingers; and this is also the same basic principle behind the bistable silicon impulse spring in the Girard Perregaux Neo Constant Escapement.

Pressing the upper start/stop pusher causes the upper and lower ends of the blade to flip positions. The upper lobe (red) snaps counterclockwise; the lower lobe snaps clockwise. The lower lobe, as it moves, opens the jaws of the vertical clutch, allowing the clutch wheel to snap into position and begin to drive the chronograph seconds (and minute) recorders.

Note that the upper lobe has a pin on it (visible in the first image of the switching mechanism) that pushes on a rotating lever on the same axis as the axis of rotation of the upper blade spring lobe. This lever rotates counterclockwise, which causes the horizontal blade springs in the reset hammer to flip convexities so that they now face upwards. In doing so, they lift the reset hammer off the heart pieces, allowing the seconds and minute recorders to rotate.

Chronograph Stop

Stopping the chronograph disengages the vertical clutch, but allows the reset hammer to remain in its position, lifted off the heart cams, so that elapsed time can be read.

Pressing the upper start/stop pusher again, flips the bistable blade (red) back into its first position. This allows the jaws of the vertical clutch to close, lifting the chronograph driving wheel out of engagement with the chronograph seconds wheel, stopping the chronograph.

Also note that the rotating lever controlling the compliant springs of the reset hammer, does not change position. This is because the pin on the upper lobe of the red compliant spring can only act in one direction (that is, it can only push the lever counterclockwise). Dropping the reset hammer onto the heart pieces would require the rotating lever to rotate clockwise, so that the control lever comes back in contact with the pin.

Chronograph Reset To Zero

That’s where the reset pusher comes in. Pressing the reset pusher moves a long lever, shown in the diagram below in outline on the left; this lever rotates to the left at its upper tip. In doing so, it makes contact with the control lever for the reset hammer, pushing on its lower extension. This causes the reset hammer’s compliant springs to flip convexities again, snapping the reset hammers down onto the heart cams, resetting the recorders to zero.

If you look at the first image of the chronograph switching mechanism, by the way, you’ll see that there’s a lever on the reset hammer which controls the position of the jumper spring that holds the minute recorder in place. As the reset hammer flicks downwards to reset the heart pieces to zero, this lever lifts the jumper spring out of engagement with the minute recorder gear teeth, allowing the gear to rotate back into its zero position.

The mechanism is most ingeniously designed. It has very few moving parts, and the use of the bistable switching mechanism ensures repeatably precise action in starting, stopping, and resetting the chronograph. The forces in the switching mechanism, thanks to the use of flexible bistable components, is identical at every phase of operation and not dependent on pressure on the pushers. In particular, the combination of bistable components with switching levers operated on by undirectional pins, allows the mechanical state changes between start, stop, and reset to be executed cleanly, and with the most efficient distribution of mechanical forces. There appears to be nothing to go out of adjustment; this is a most interesting use of LIGA fabrication to produce a system of mechanical linkages which would have been difficult or impossible with traditional watchmaking materials.

For most of the history of the chronograph, there have been only a small number of technical solutions. Clutch systems are largely divided between lateral clutches and their variants, and vertical clutches and their variants; for actual control systems, we really have only two up until now – the column wheel, and the lever and cam system (used, to pick a famous example, in the caliber 861/1861 used in the Speedmaster, and more widely in the Valjoux 7750). A net new chronograph switching system is pretty big news, and it takes long enough to develop a new one that you might consider yourself lucky to have been around for this one. It’s a fascinating mechanism; apparently simple, but elegant and subtle in its action, and a major development for TAG Heuer and the industry overall.

The Tag Heuer Monaco Evergraph: case, 40mm, in grade 5 titanium or grade 5 titanium coated with DLC; water resistance 100M. Dial, transparent acrylic glass; applied indexes with Super-LumiNova. Movement, TAG Heuer caliber TH80-00, 32mm x 32mm overall, shaped caliber, chrongraph with TH-Carbontime carbon balance spring and oscillator; freesprung adjustable mass balance; novel chronograph switching system using bistable LIGA fabricated components, running at 36,000 vph/5Hz in 47 jewels with 72 hour power reserve. Price, $25,000.

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