Founded by the Netherlands-based brothers Bart and Tim Gronefeld, their eponymous brand carries a legacy of watchmaking that dates back to 1912, bringing a wealth of expertise to each meticulously crafted timepiece. Combining contemporary aesthetics with classical mechanics, Gronefeld’s design language culminates in watches that are not merely timekeepers but wearable pieces of art. The Gronefeld One Hertz is a horological masterpiece that exemplifies the Gronefeld's dedication to precision and innovative design. Encapsulated within a durable titanium case boasting angular lugs and a thin bezel, the One Hertz aims to highlight its most unique function, its dead-beat seconds hand. A rarity in mechanical timepieces, the dead-beat seconds hand beats once per second, much like a quartz watch, while being powered by a mechanical movement that has had to be slowed down in order to beat as slowly as it does – a technical nightmare. Launched as a collection of 30 pieces, the Gronefeld One Hertz showcase's the brothers’ technical ingenuity and passion for pushing the boundaries of traditional watchmaking by creating exclusive, handcrafted watches that offer a unique story and an exceptional experience for the wearer.

The One Hertz Titanium

The One Hertz Titanium features a high-tech, polished and brushed titanium case as well as a fresh white micro-guilloched dial. Available in a limited edition of 30 pieces in polished and brushed grade 5 titanium.

History of Dead Seconds

With the introduction of the pendulum in the 17th century, clocks finally became accurate enough to measure seconds. It was not long before a hand indicating seconds on a long clock’s dial signified a precision timepiece. A pendulum with a period – the time to swing forward and back – of two seconds (the most common) resulted in a single tick per second.

The invention of the balance spring, which replaced the pendulum, enabled miniaturisation. As portable pocket watches became more accurate, watchmakers naturally thought to copy the one-second steps of the seconds hand which signified a precision timepiece. However, the rapidly oscillating balance meant that it could not be directly driven as with the pendulum, so it required either a new mechanism if independent, or be driven from another complication e.g. constant force device. While pocket watches have featured independent dead seconds in the past, the Grönefeld One Hertz was the first series wristwatch to feature independent dead seconds.

The Grönefeld One Hertz is unique among wristwatches in that its dead seconds are powered by a secondary gear train, independent of the gear train for the hour and minute indications.

One Hertz

The hertz (symbol: Hz) is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. This SI unit is named after Heinrich Hertz. One Hertz simply means “one cycle per second”.

The second (SI symbol: s), sometimes abbreviated sec., is the name of a unit of time, and is the international base unit of time. To highlight the SI seconds, the One Hertz displays dead seconds with a large seconds hand in its own dial. Hours and minutes are non-SI units of time because they do not use the decimal system so are displayed separately.

Mechanical wristwatch movements often have balance frequencies of 2.5 to 5 hertz, which results in the seconds hand making tiny steps of 5 to 10 steps each second and looking like a smooth movement. The seconds hand of the One Hertz is either stationary (dead) or jumping in a full one-second increment each second.

The “One Hertz” independent dead seconds complication

Displaying dead seconds in a wristwatch without a constant force device is no easy task. The friction of the mechanism has to be absolutely minimal so it does not interfere with the escapement.

Bart and Tim Grönefeld used an independent dead seconds mechanism that is driven from its own secondary gear train with its own power supply. The seconds are driven from one mainspring barrel and the hours and minutes from another. Friction is with this system guaranteed to an absolute minimum and the complication has no adverse influence on the escapement and free sprung balance.

The two mainspring barrels are wound simultaneously from the crown, which features an innovative “push to set”, “push to wind function”, with the mode selected indicated at 3 o’clock. A power reserve indicator at the top of the dead seconds dial keeps track of the 72 hours of autonomy.

Biography: Bart and Tim Grönefeld

The name Grönefeld and the art of watchmaking have a family history spanning a hundred years, originating in the ancient town of Oldenzaal in the Netherlands. There, in a shop facing the ancient basilica church from 1240, Johan Grönefeld, Bart and Tim’s grandfather, began his career as a watchmaker in 1912, marking the beginning of the highly talented dynasty of Grönefeld watchmakers that continues today.

Bart and Tim’s workshop is located in Johan Grönefeld’s original building, representing a continuous, unbroken watchmaking family history that is exceptionally rare to find anywhere in the world today.

Bart and Tim underwent extensive training in Switzerland, and within a relatively short span of time proved themselves adept world specialists in the production of the most coveted and exquisite horological complications of all: the tourbillon and the minute repeater wristwatch. In 2008, after working anonymously behind the scenes for prestigious Swiss brands, they presented the first watch bearing their own name, the GTM-06 Tourbillon Minute Repeater.

In 2010, Bart and Tim presented their second watch, the One Hertz, the world’s first series wristwatch with independent dead seconds and featuring a completely new movement, the G-02 Calibre. The One Hertz Classic collection has grown to include the One Hertz 1912, One Hertz Dune, One Hertz Ruthenium, One Hertz Titanium and One Hertz Platinum, while the Contemporary collection, launched in 2012, includes the One Hertz Fire and the One Hertz Ice. In 2013, the open-dial One Hertz Techniek was launched.

The One Hertz is a prize-winning timepiece. It was awarded the Innovation prize in the 0024 WatchWorld Watch of the Year contest in 2011 and was voted Watch of the Year in 2011 by members of the influential watch forum Timezone.