This steel 1912 One Hertz is one of the earliest wristwatches made by the Grönefeld brothers, after their Tourbillon Minute Repeater. Designed by the family watchmaking duo in the Netherlands, the One Hertz movement was realised with the assistance of famed complications specialist Renaud and Papi in Switzerland, where Bart and Tim Grönefeld spent many formative years at the heart of the manufacture. Though subsequent watches have since been made in different case materials, the One Hertz was initially launched as limited production of just 12 steel pieces in 2010.

One of the more obscure complications in horology, the 1912 One Hertz incorporates deadbeat seconds. An interesting one for the brothers to tackle so early on in their career, the original deadbeat escapement goes all the way back to 1675, when it was invented by Richard Towneley for use in regulator clocks at the Greenwich Observatory. The complication itself is demonstrated through jumping seconds snapping into position, contrary to the majority of mechanical watches where the second hand glides smoothly between passing seconds. As specialists in complicated watches, the Grönefeld’s intent to follow their Tourbillon Minute Repeater with a simple, time-only watch was always destined to evolve into something mechanically more intriguing.
 
In a traditional fashion, the Grönefelds imagined their desired dial layout first, before figuring out how to make a suitable movement to match. The deadbeat seconds occupies a central place, emphasised through the large seconds sub-dial - a sapphire disc raised above the other indications with metallic accents. In comparison, the subsidiary dial for the hours and minutes is discretely located above, extending within the seconds indication. The overlapping portion of the sapphire disc is transparent so as not to obscure the hours and minutes.
 
Encased within the large seconds sub-dial is the recessed power reserve indicator, highlighted by a frosted surface. The crown position indicator for “winding” and “setting” is similarly textured. Toggling between the two modes involves using the push-button crown, hacking the movement during setting - a system reminiscent of the clutch mechanism found in a number of Richard Mille models, made early on by Renaud et Papi.
 
In the case of the One Hertz, Bart and Tim designed their movement to operate using two gear trains, based on two synchronised spring barrels feeding two separate (but linked) movements – one for the hours and minutes and the other for the seconds. According to Bart Grönefeld, the parts for the One Hertz movements were machined by Renaud et Papi in Switzerland, before being shipped to the Netherlands to be finished, painstakingly decorated, and assembled in the Grönefeld workshop. The movement features over a dozen different finishing techniques, from snailing to frosting. The bridges, shaped like the bell gable roofs of Dutch houses, are fashioned out of steel, which is much more difficult and costly to work with than brass or silver.
 
Each individual bridge requires dozens of steps and up to ten hours of work, including mirror polishing of the screws, and chamfering rims and slots, demonstrating the brothers’ fascination with depth and light. The overall dimensionality is reminiscent of A. Lange & Söhne, or even fellow Renaud et Papi alumni Greubel Forsey.
 
The case, measuring 43mm across and 13mm thick, is made out of stainless steel. It features brushed case sides, with polished caseback and bezel portions, giving the One Hertz a classically finished appearance. Despite its imposing size, it wears comfortably on the wrist, owing to the choice of case material and downturned, sculpted lugs.

If sold within the United Kingdom, this Grönefeld One Hertz 1912 will be subject to 20% VAT

Closer look

Condition

This Grönefeld One Hertz 1912 is in excellent overall condition. The case and lugs show virtually no signs of wear throughout and have likely been worn on only a handful of occasions, if at all. The dial, hands, and movement show no signs of imperfections. The engravings on the buckle are crisp and well defined.

Warranty

The watch comes with a two-year warranty from A Collected Man, alongside a lifetime guarantee of authenticity.