Grönefeld presenting the “One Hertz Techniek”


The world’s first independent dead seconds series wristwatch –
now with a revealing open dial to showcase the complex mechanics within

The “One Hertz Techniek”
Bart and Tim Grönefeld present the One Hertz Techniek, the world’s only series wristwatch with independent dead seconds, featuring a stunning, open-work dial that showcases the intricate upper mechanics of Grönefeld’s own proprietary movement, the calibre G-02.

While the dial is dominated by a large dead seconds chapter ring in sapphire, the other indications, bridges and Grönefeld logo are crafted in stainless steel, which is relief engraved, bevelled and finished completely by hand.

The open dial is framed by a gleaming high-tech Grade 5 titanium case available in two versions: natural polished and brushed titanium or black DLC – when the timepiece becomes the “One Hertz Techniek Nocturne”. Both versions feature the Grönefeld’s own ergonomic winding and setting mechanism, selected by simply pushing the crown in, rather than pulling it out.

One Hertz Techniek – the clue is in the name, the beauty in the mechanics
Dutch watchmakers Bart and Tim Grönefeld chose the name 'Techniek' for a very simple reason. “Here, we have made the One Hertz’s movement and mechanics more visible than ever with an open-work dial,” they say. “The technicality of the movement is really on show, so we called it the One Hertz Techniek, because ‘techniek’ is the Dutch for ‘technical’.”

The open dial is such that the mechanics behind each one of the One Hertz’s indications and signature features are subtly – and beautifully – revealed.

At the heart of the hour and minutes subdial at 2 o’clock, we see the hour wheel – logically rotating in 60 minutes – offering a splash of colour and contrast to the largely monochrome movement.

The independent dead seconds – where the second hand advances in full steps of one second instead of the more usually smooth sweeping action of mechanical seconds – features prominently in a large subdial at 7 o'clock. The open dial affords rich views of the large, stainless steel gear train bridge for the dead seconds mechanism, the dead seconds escape wheel and the centre wheel. At the top of seconds dial at 11 o’clock, the lever and spring of the power reserve indicator can also be seen.

The whole ensemble of indications and exposed mechanisms are set off against the dark texture of the hand-frosted mainplate and bridges.

Turning over the One Hertz Techniek completes the mechanical feast for the eyes with the sumptuous display back featuring no fewer than nine finely-crafted stainless steel finger bridges. The One Hertz is the world’s first series movement with all the bridges in stainless steel.

The “One Hertz Techniek” is a limited edition of 30 pieces in Grade 5 titanium, with either a natural finish (“One Hertz Techniek”) or black DLC coated (“One Hertz Techniek Nocturne”).

Winding-Setting mechanism and hacked seconds
With the One Hertz, winding and setting are selected by pushing the crown in, instead of pulling it out – a very ergonomic system. The winding-setting (W S) indicator at 3 o’clock provides a neat visual signal as to the mode selected, and the winding-setting lever and its spring are visible around the indicator thanks to the open dial. What’s more, the counter-poised seconds hand can be ‘hacked’ – i.e. stopped – when ‘setting’ is selected, to ensure maximum precision when adjusting the time.

The “One Hertz Techniek” and the “One Hertz Techniek Nocturne”
While the One Hertz Techniek is available in polished and brushed natural Grade 5 titanium, Bart and Tim Grönefeld have harnessed the talents of Finnish company DIARC, world-renowned for their coating techniques, to offer a striking black DLC coated version as well. Bart and Tim have dubbed this black version the “One Hertz Techniek Nocturne” after ‘nocturne’, the style of painting that depicts scenes evoking night.

Dead seconds
The dead seconds complication was a very respected mechanical complication until the 1980s because it denoted superlative accuracy. It was traditionally derived from other mechanisms such as a constant force device or remontoir d’égalité.

However, the popularity of dead seconds faded with the dominance of quartz movements, which also stepped in full seconds. A smooth sweeping second hand came to differentiate mechanical from quartz.

But with the One Hertz and its unique secondary gear train, Bart and Tim Grönefeld have resurrected this long-neglected complication and re-positioned it where the complication originated – on the pedestal of high precision.

The stepping movement of the large second hand of the One Hertz subtly signals its unique mechanism, imperceptible to most, but obvious to haute horlogerie connoisseurs, who will appreciate the sublime, flawless fine-finishing of all 285 components of the calibre G-02 movement.










Specifications (Click to slide)

The “One Hertz Techniek” is a limited edition of 30 pieces  

Features and indications

  • Independent dead seconds – large dial at 7 o’clock
  • Hour and minutes – subdial at 2 o’clock
  • Power reserve indicator at 11 o’clock
  • Innovative Winding-Setting mechanism
  • Winding-Setting indicator at 3 o’clock
  • In-house calibre G-02

Case and dial

  • Case material: Grade 5 polished and brushed titanium and black DLC (Diamond Like Carbon) coating
  • Engraving: “Titanium”, “Limited 30 pieces” and the serial number
  • Screws: Stainless steel security screws
  • Case dimensions: 43 mm x 12.5 mm
  • Sapphire crystals: Top domed with antireflective treatment both sides; flat display back with antireflective treatment on both sides
  • Water resistance: 3atm/30m/100 fee
  • Crown: Titanium, black DLC coated with engraved “G” logo and push to set/wind function
  • Dial: Stainless steel open dial. Relief engraved, bevelled and finished by hand
  • Hands: Hours and minutes, large counter-poised seconds, power-reserve and setting-winding
  • Strap and buckle: Hand-sewn matte black, alligator leather with steel tang buckle black DLC coated (Nocturne), Grönefeld logo 


  • Calibre G-02: Mechanical hand winding, independent dead seconds, power reserve indicator and setting mechanism indicator.
  • Dimensions: 34mm x 9.5 mm
  • No. of parts: 285
  • No. of jewels: 39 jewels set 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: 9.12 mm free sprung variable inertia balance wheel Balance frequency: 21’600 bph / 3Hz
  • Balance spring: Phillips terminal overcoil curve, triangle-style stud
  • Escapements: Swiss lever escapement and unique dead seconds escapement
  • Main Plate: Hand frosted and spotted black rhodium plated nickel silver
  • Bridges: Stainless steel hand bevelled, micro-blasted, circular grain on the top, relief engraved on micro blasted surface
  • Gearing: 2 independent gear trains each with their own energy sources (2 barrels)
  • Dead seconds mechanism: Independent mechanism, cam with 30 teeth on the going gear train on the fourth wheel, escape wheel on the fourth wheel of the independent gear train, unique double lever with 4 jewelled pallets 
  • Winding-Setting mechanism: Push function crown for winding or setting 
  • Power reserve mechanism: Classic Breguet style by means of a cone moving up and down on the threaded barrel arbour




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