Faithful to the original model, the Spirograph Sport highlights the tourbillon’s function. Visible through a broad dial aperture at 6 o’clock, this one-minute tourbillon is equipped with an escapement designed and developed 100% by the KF brand, as is the rest of the movement that drives it. The result is an entirely Swiss Made watch produced in La Chaux-de-Fonds.

This calibre has been designed and built around its balance-wheel to meet the standards of pure chronometric performance: an extremely rare event in the industry. With that in mind, this chronometric heart comprises two new innovations and was shaped by the vision and expert hands of a watchmaker, precision timer and construction developer driven by passion and conviction.

A precision instrument intended for daily use, this manual-winding calibre beats at a rate of 18,000 vibrations per hour. While making it more difficult to adjust the regulating organ, this frequency enables better management of the energy required for the watch to operate properly. It also reduces component wear and tear, thereby enhancing sustainability of precision. Thus, through the choice of materials and the specific construction of the calibre, the Spirograph Sport will be a lifetime companion and survive through subsequent generations, providing it is regularly serviced.

Equipped with a new elastic suspension system, the movement – which appears to be “flying” inside its case – can absorb shocks of up to 5,000 Gs. It displays considerable endurance with a 70-hour power reserve, meaning that it operates during this time period without requiring any manual winding via the crown. However, in order to improve chronometric accuracy, autonomy is deliberately reduced to 44 hours by means of the “Maltese cross” stopwork mechanism, which guarantees a more stable driving force.

While the KF brand is synonymous with fine watchmaking, it devotes its keenest attention to chronometry – the term used to designate high-precision time measurement.

It all began a few years ago with the construction of the first rim-free balance-wheel featuring two round peripheral weights held by a dedicated arbor. While this resolutely innovative design is above all a nod to marine chronometers, which also worked with large balance-wheels, it is also a reference to chronometry and its origins.

Based on this new balance-wheel, two new innovations enrich this ongoing quest for precision. The first concerns a recurrent problem in watchmaking: thermal coefficient, or the expansion of certain components during temperature changes. This is a major challenge, especially when it impacts the components that form the heart of the watch, in this case the regulating organ. A temperature increase of a few degrees influences the balance-wheel, which expands outwards, sometimes causing a loss of several seconds. This phenomenon is partially compensated by the balance-spring which tends to generate a time gain. For decades, traditional watchmaking has therefore used what are known as “self-compensating” balance-wheels, thereby substantially mitigating expansion-related phenomena. This new construction makes it possible to take a step forward by creating a balance-wheel capable of providing compensation described as “auxiliary”, in order to further reduce the impact linked to the thermal coefficient not resolved by a traditional self-compensating balance-wheel.

This new balance-wheel, made of non-magnetic steel, can withstand an inertia of 85 gr/mm2 and has a hardness of up to 600 Vickers. It is therefore more resistant to shocks.

In practice, the balance-wheel plate forms one arbor crossing through the centre of the balance-wheel, thus enabling an extension of the material in the event of a temperature increase. This extension is contained by a second arbor (the bar), which remains invariable. Therefore, when the material expands, the force is redirected to the affix arms. Each arm is solidly attached to the invariable arbor by a screw-fitted pivot point enabling the balance-wheel to move inwards. The affix arms can then accommodate, at different places, a certain number of screws (of different sizes and materials) making it possible to influence the effective mass, thus offering the watchmaker the possibility of working on the variations of inertia related to the thermal coefficient. This is the so-called “auxiliary compensation” principle. Located opposite the affix arms, two auxiliary classification weights serve to adjust the variable weight of the balance-wheel. Their purpose is to compensate for the weight of the screws placed on the two affix arms so that the balance-wheel is neither too heavy nor too light. Moreover, given that every detail counts, their surfaces can be personalised (notably by engraving or gemsetting). Finally, a third arbor, perpendicular to the first, is fitted on either end with two screws, enabling fine adjustments on the one hand, as well as classification of the balance-wheel at 18,000 vibrations per hour.