Timekeepers Club / August 15, 2023

Armin Strom Gravity Equal Force Only Watch 2023

For the 10th edition of the biennial Only Watch charity auction, the Biel/Bienne-based independent watch brand Armin Strom has created a unique edition of its successful Gravity Equal Force, the world’s first automatic watch with a constant force transmission.

This unique iteration of the Gravity Equal Force ‘Ultimate Sapphire’ incorporates the promotional colors of the 2023 Only Watch event, with relevant details including a transparent green sapphire dial, a red logo and blue stitching on the included custom strap. The one-of-a-kind timepiece offers an extraordinary view of the exquisitely finished manufacture movement, which features superior chronometric performance and exceptional hand-finishing, with a contemporary expression made in-house by Armin Strom’s master artisans.

For Armin Strom’s master watchmaker and co-founder Claude Greisler, the green yet transparent dial of the Gravity Equal Force Only Watch 2023 makes perfect sense. “Green is the colour of hope. And hope is important when it comes to this terrible disease for children,” he says, hoping the donated watch will bring a good contribution to Only Watch, the organisation which since 2005 has raised nearly CHF 100 million to accelerate the research on Duchenne muscular dystrophy.

Together with surrounding colourful details, the off-centre sapphire dial forms a deconstructed rainbow, which shares the dial-face attention with Armin Strom’s signature tri-bridge design. This holds the microrotor, the winding mechanism and the patent pending Equal Force Barrel, an example of Armin Strom’s relentless quest to improve timekeeping. This innovation provides consistent power from the mainspring to the balance wheel, thus always ensuring flawless and constant precision during the power reserve.

The Gravity Equal Force Only Watch 2023 features everything that passionate watch collectors around the world have come to associate with Armin Strom: extreme accuracy, contemporary and architectural design, and an open-worked dial revealing mechanical dreams where all parts – even the invisible ones – are decorated by hand by Armin Strom’s in-house master artisans.

They demonstrate an extreme devotion to traditional haute horlogerie watch decorations, including polished bevels, black polishing, polished sinks, perlage and various grainings. This is combined with a contemporary architectural design approach, which is clear in the signature tri-bridge, coated with dark grey ruthenium. These bridges are fixed with mirror-polished screws on the black movement plate, which is hand-guillochéd by Kari Voutilainen’s atelier – the only part decorated by an outside friend of Armin Strom.

The Gravity Equal Force movement, completely developed and manufactured in-house by Armin Strom, is the world’s first automatic watch movement with a constant force transmission. The invention by Mr Greisler and his team is a unique stop declutch mechanism, which combines a Maltese cross, a technical solution normally found in hand-wound pocket watches, with an automatic winding system. The main principle is the same: a Maltese cross inside the barrel controls the mainspring and stops it from fully unwinding. Armin Strom’s Maltese cross is, however, also declutched when the rotor has given the mainspring its optimum tension – a world first. By cutting the top and the bottom parts of the power reserve, a constant force is delivered with an extremely secure, stable and precise amplitude and isochronism throughout the entire cycle.

The isochronal dilemma of using a fully wound mainspring throughout its whole cycle can be symbolised with a toy car,” Claude Greisler explains. “You remember the type that you pull backwards and release? First it speeds off like crazy, then it reaches its normal speed, followed by a slowdown before coming to a halt. With such a cycle you may have a good intermediate precision, but in the beginning your watch will be too quick, and in the end it will be too slow. With our solution, the accuracy is consistent throughout all 72 hours of power reserve, which is shown on a discreet indicator on the Equal Force barrel itself.

Armin Strom is all about innovation connected with the science of movements,” says Serge Michel, founder of Armin Strom, who fully supports the mission of Only Watch founder Luc Pettavino. “When Luc asked us if we wanted to create a watch for him, we said: ‘Definitely, we are in.’ In 2023, we are donating a unique timepiece for the fifth time, and I salute that the auction is open to the whole watch industry, thus uniting the community for something good. With the Armin Strom Gravity Equal Force Only Watch 2023, we are not only supporting an important cause, but have also created something wonderful for passionate collectors desiring something unique."

Technical specifications

Armin Strom Gravity Equal Force Only Watch 2023

Reference: AS/ID ST23-GEF.SA.M.TX.N4

One-off piece for Only Watch 2023


  • Material: Stainless steel
  • Diameter: 41 mm
  • Height: 12.65 mm
  • Sapphire crystal and case back with antireflective treatment
  • Water-resistant to 3 ATM

Dial and hands

  • Dial: Green-toned, off-centre sapphire dial with subdial
  • Hands: Manufactured by Armin Strom – steel with hand-finishing and Super-LumiNova® filling


  • Armin Strom manufacture Caliber ASB19
  • Automatic winding with microrotor, Geneva drive Equal Force barrel, offset display with subdial seconds
  • Regulating system: Balance wheel with four regulating screws
  • Dimensions: 35.52 mm × 11.67 mm
  • Frequency: 3.5 Hz (25,200 vph)
  • Finishing: Hand-finishing of the highest quality level
  • Number of jewels: 28
  • Number of components: 202
  • Power reserve: Geneva stop-work limited to 72 hours


  • Hours, minutes, seconds, power reserve indicator

Strap and buckle

  • Delivered with a black fabric strap with blue stitching and stainless-steel double folding clasp


  • CHF 15'000 – 30'000
  • USD 16'500 – 33'000
  • EUR 15'500 – 30'900

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