The calibre 201.0/201.1 of the ATUM Pure is a pillar movement consisting of the main plate and the typical 2/3 plate. A glance through the display back reveals the unusual appeal of Grossmann’s Pure Classic Finish. Specially developed for the steel case of the ATUM Pure, the calibre showcases purity in materials and straightforward execution.
The untreated German silver plates are shot-peened with glass beads. This technique matts the surface and makes it sensitive, so great care is called for in the assembly process. Rather than with decorative chatons, the white sapphire bearing jewels are pressed directly into the plate and sparkle thanks to their chamfered seats. Flat polished movement screws with the original sheen of steel accentuate the monochrome allure. The focus is on the multicoloured oscillation system.
The calibre 201.0/201.1 movement directs the observer’s attention straight to technical details. In the oscillation system, the Grossmann balance is paired with a hand-bent flat hairspring. To fine-tune the frequency of the oscillator, the inertia screws in the balance wheel rim can be exchanged crosswise with screws from one of the five different mass categories.
Instead of forming the adjuster curve of the flat balance spring using a fixture, the material is carefully bent out by hand to keep the curb pin free. The outer attachment point is specially modified for the flat hairspring. It receives a double bend before being pinned to the stud. This bend allows the adjuster curve to be accurately centred.
The calibre 201.0/201.1 provides convenient options for adjusting the oscillation system; they are superior in design to conventional solutions.
The beat and rate can be adjusted separately with a micrometer screw and without removing the oscillation system. For this purpose, the cantilevered balance cock is fitted with a rotatable stud holder. In the calibre 201.0, the bearing and thus the guide element of the stud holder were elaborately optimised. The beat of the oscillator can be adjusted by moving the index tail. By tightening a clamping plate, the stud holder can be easily immobilized so that moving the index tail now adjusts the rate of the oscillator.
There is absolutely no play between the index adjuster, the stud holder, and the upper balance bearing. This allows the ATUM Pure to be precisely adjusted at all times.