Armin Strom is an independent watchmaker — with a small manufacture in the Swiss watchmaking hub Biel/Bienne — that makes high-quality timepieces with unique complications and superb finishes.

With current production in the 400-500 watches per year range, you’re assured that each watch is manufactured to very high-quality specifications and that you’re getting a product that not many other people will have. At the same time, the company is expanding, so you know you’re buying into a brand that’s progressing. 

Armin Strom Gravity Equal Force Ultimate Sapphire

As you likely know if you follow Professional Watches’ coverage of Armin Strom, the company collaborates with renowned artisan watchmaker Kari Voutilainen’s workshop to craft special handmade guilloché dials and mainplates. And yes, the Gravity Equal Force Ultimate Sapphire is one of those special Kari Voutilainen collaboration timepieces. In this instance, the mainplate features a gorgeous dark gray guilloché plate, created using a hand-operated rose engine lathe machine.

Originally debuted in September 2021, the Gravity Equal Force Ultimate Sapphire is a special version of the Gravity Equal Force timepiece, that was originally announced in 2019 at Watch Time New York, and that we reviewed in 2021 — which represents the world’s first automatic watch equipped with constant power transmission. Constant power ensures higher precision throughout the entire power reserve by evening distributing the power to the balance wheel, balance spring, and escapement. Thanks to a patented stop-work declutch (disengagement) mechanism combined with an automatic winding system for the first time, the energy released from the Equal Force mainspring barrel is constant and smooth, enhancing chronometric precision.

Armin Strom Gravity Equal Force Ultimate Sapphire wristshot

A mainspring is a tightly coiled band of metal found in a watch’s barrel to give power to the movement. However, the force exerted by a mainspring in a normal watch during winding can never be delivered consistently, since the force provided at full draw is necessarily greater than towards the end of its power reserve. The patented “stop work” mechanism in the Gravity Equal Force prevents the mainspring from fully unwinding, thereby only utilizing the part of the mainspring unwinding process that can deliver power most evenly. To fully understand the technological aspects, our master watchmaker Jordan Ficklin did an in-depth technical review of Armin Strom’s caliber ASB19 earlier this year.

Aesthetically, the bridges have been coated with dark gray ruthenium, and the mainspring barrel, which has a power reserve indicator showing how much of the 72-hour power reserve is remaining, as well as the micro-rotor has a brighter contrasting rhodium finish. The components are both machine and hand-finished, including anglage, creating an impeccable final product that rivals watches costing far more.

Armin Strom Gravity Equal Force Ultimate Sapphire

Lastly, the “Ultimate Sapphire” refers to the off-center dial which is made of a thick sapphire crystal that has the hour and minute scales printed in white on the surface, and a frosted white small second subdial between 7 and 8 o’clock. The hours and minutes are indicated with stainless steel luminous lance-shaped hands manufactured and finished by hand in-house. And small seconds hand is baton-shaped and is also in-house made.

Presented in a conservatively sized 41 mm x 12.65 mm (48.1 mm lug-to-lug) stainless steel case, the watch proportions will look attractive on a broad variety of wrists. Completing the sporty high-tech look, the Gravity Equal Force Ultimate Sapphire is paired with a black textile strap (20 mm/ 18 mm) with contrasting thread and is secured with a stainless steel pin and buckle or double folding deployant clasp.


The cost of the Gravity Equal Force Ultimate Sapphire (Ref. ST21-GEF.SA) has risen to a retail price of $25,000 which is a $2,100 increase since it debuted last year, and while as a consumer you wonder what the justification is for any rise in prices, this is one of the most exclusive timepieces made by Armin Strom. With the Voutilainen mainplate, off-center sapphire crystal dial with frosted sapphire subdial, and innovative stop-work constant force functionality, you can be certain that even in an industry where outsourced movements and derivative watch designs are the norms — few will compare to this.

Learn more at Armin Strom.

Posted by:Jason Pitsch

Jason is the founder of Professional Watches and specializes in writing, product photography, and digital marketing.