Photo essay: Grönefeld One Hertz with independent dead seconds (with pricing)

Dutch brothers Tim and Bart Grönefeld are independent watchmakers based in the town of Oldenzaal. Before striking out on their own, the Grönefeld  brothers worked at Renaud & Papi. Their first product was a minute repeater using a Christophe Claret base movement. However, it is their second timepiece, the One Hertz, that really caught collector's attention.

Grönefeld One Hertz Platinum

Characterised by the large seconds sub-dial, with a smaller subdial at one o'clock for the time, the One Hertz is an independent dead seconds watch. That because the dead seconds has its own power source and transmission, thanks to the twin barrels and gear trains, one for the time and the other for the dead seconds. This is a more elaborate dead seconds than is usual; the traditional dead seconds mechanism has a separate gear train but not mainspring.


Developed by the brothers themselves, the G-02 movement of the One Hertz features another unusual feature - it has a function selector crown. Rather than pulling out the crown as is convention, the user just needs to push the crown to either set or wind the watch. The function selected is then indicated by a small display on the dial, "W" for wind and "S" for setting.

Grönefeld One Hertz Ruthenium with titanium case

Notably, the bridges of the movement are steel, which is a harder material than the typical bridge alloys of brass or German silver.

Despite that the brothers manage to achieve a striking level of finishing, with wide, polished bevels on the bridges that contrast well with the frosted and brushed bridge surfaces.

The grey tone of the bridges makes the jewels in gold chatons, laid out in an almost circular manner around the movement, even more prominent.

Bridges aside, the rest of the movement demonstrates a high level of attention to finishing, right down to the perlage on the base plate.

The beautifully finished cock for the dead seconds pallet fork

In the interests of chronometry, the One Hertz has a large, free sprung, adjustable mass balance with a Philips terminal curve hairspring.

That quality extends to the external components as well. The lugs, for instance, have polished bevels, while the crown is well rendered in relief.

And the dial has two levels, with the oversized seconds dial surrounded by a raised sapphire ring with chemically deposited metal markers.

The One Hertz is available in several case metals, all of which are 43 mm wide and 13 mm high. This is a sizeable watch but it wears well thanks to the curve of the lugs. 

Admittedly the dial design is not quite my cup of tea, because it strikes me as being somewhere in between modern and classical, but not quite either.

But that is a purely personal observation. Objectively, the fine fit and finish of this watch is undeniable, as is the atypical execution of the dead seconds.

The price of the platinum One Hertz is EUR79,500, while the rose gold is EUR55,500 and the titanium is EUR44,500 - all pricing is before tax.

- SJX

Grönefeld One Hertz Dune in red gold