The Grönefeld One Hertz Hands on

We had the privilege on Basel World to see the new One Hertz. The Grönefeld One Hertz is the world’s first and only series wristwatch with independent dead seconds. It features a beautiful solid silver dial and entirely in-house developed movement with stainless steel bridges and exceptional fine finishing.


With dead seconds – secondes mortes in French – the seconds hand advances in full steps of one second instead of the usual smooth sweeping action of mechanical seconds. Dead seconds was a very respected mechanical complication because it denoted superlative accuracy. However, the popularity of dead seconds faded in the 1970s and 80s with the dominance of quartz movements, which also stepped in full seconds. Mechanical movements soon became distinguished by a smooth, sweeping seconds hand.

Grönefeld One Hertz

With the One Hertz, Bart and Tim Grönefeld have resurrected the long-neglected horological complication of dead seconds and re-positioned it on the pedestal of high precision. The Grönefeld One Hertz is unique among wristwatches in that its dead seconds are powered by a secondary gear train, which is completely independent of the gear train for the hour and minute indications. Until the arrival of the One Hertz, dead seconds was usually derived from mechanisms requiring considerable force from the going train. This resulted in more wear and less energy available to the escapement.


The large seconds hand of the One Hertz subtly signals its unique mechanism, imperceptible to most, but obvious to haute horlogerie connoisseurs who will appreciate the flawless hand-finishing of all 285 components of the calibre G-02, Grönefeld’s own proprietary movement.


While the dial is dominated by the over-sized dead seconds, elegantly shaped blued-steel hour and minute hands make for easy reading of the time in the sub dial at 2 o’clock. The hour/minute sub dial is nicely balanced on either side by a power reserve indicator at 11 o’clock and a winding-setting (W-S) function indicator at 3 o’clock. Winding and setting are selected by pushing the crown in, instead of pulling it out – a very ergonomic system – and the winding-setting indicator provides a neat visual signal of the mode selected. What’s more, the counter-poised seconds hand ‘hacks’ – i.e. stops – when ‘setting’ is selected, to enable maximum precision when setting the time.


The dial is crafted out of solid sterling silver then blasted with brass particles to attain a frosted finish with a very slight sparkle. A thin layer of transparent lacquer is then applied to prevent tarnishing. The soft sheen contrasts superbly with the flamed-blued hands, making for excellent legibility. The graceful arcs and curves of the displays are complemented by the three-dimensionality of the multi-layered dial. The ensemble is beautifully framed by the highly-polished red gold case and bezel.


All applied dial elements, including the dead seconds chapter ring, are rhodium plated with circular graining and beveled edges. The bevels are polished with diamond paste to a brilliant gloss, creating scintillating reflections of light echoing the high-end finishing of the stainless steel movement bridges visible through the display back.


The One Hertz is a prize-winning timepiece. It was awarded the Innovation prize in the 0024 WatchWorld Watch of the Year contest and was voted Watch of the Year by members of the influential watch forum Timezone.


The One Hertz RG is available in a 43mm red gold case.


Technical Specifications for the Grönefeld One Hertz


Features and indications

Independent dead seconds – large dial at 7 o’clock

Hour and minutes – subdial at 2 o’clock

Power reserve indicator at 12 o’clock of seconds ring

Innovative Winding-Setting mechanism Winding-Setting indicator at 3 o’clock

Solid silver dial

In-house calibre G-02


Case and dial

Case: 5N red gold case; sapphire crystal on the front is slightly domed with anti-reflective treatment on both sides; sapphire crystal on the back is flat with anti-reflection treatment on the inside; engraving of serial number and model; 8 security screws

Number of case components: 68

Case dimensions: Diameter: 43 mm; thickness: 12.5 mm

Water resistance: 3atm/30 meters/100 feet

Crown: Engraved with “G” logo and push to set/wind function

Dial: in solid silver

Seconds chapter ring:Rhodium plated with circular graining and beveled edges

Strap: Hand-sewn, alligator leather with tang buckle engraved with the Grönefeld logo



Calibre G-02: Mechanical hand-wound movement; independent dead seconds

Movement dimensions: Diameter 15 1/4’’’ 34 mm; thickness: 9.5 mm

Number of components: 285 in the whole movement

Number of jewels: 39 jewels in gold chatons

Power reserve: 72 hours

Barrels: 2 barrels, one for the going gear train and one for the independent dead seconds mechanism; both barrels are wound at the same speed and in the same direction

Balance wheel: Free sprung variable inertia balance wheel (9.12 mm diameter)

Frequency: 21’600 vph

Balance spring: Phillips terminal overcoil curve; triangle-style stud

Escapement: Swiss lever escapement

Mainplate: Spotted and snailed rhodium plated nickel silver

Bridges: Hand bevelled; stainless steel X46 Cr13 Micro-blasted centre; circular grain on the top; relief engraved in the micro blasted surface

Gearing: Two gear trains with their own energy sources (2 barrels)

Dead seconds: Independent mechanism; cam with 30 teeth on the fourth wheel of the going geartrain; special escape wheel on the fourth wheel of the independent geartrain; double lever with four jewelled pallets

Winding-setting: Crown with push function to choose between winding or setting; hacking seconds

Power reserve: Classic Breguet mechanism by means of a cone moving up and down on the threaded barrel arbour


Source Grönefeld