Brand Guides / Armin Strom / Gravity Equal Force
Reviewed by the Fine Watch Guide team · October 2026
The Gravity Equal Force, introduced in 2019 in the System 78 collection, pairs an automatic movement with a barrel stop-work and declutch so the watch draws on the more even part of its mainspring's torque range.
The Gravity Equal Force is the watch that most people have in mind when they talk about Armin Strom's engineering. It arrived in November 2019 as the first model in the System 78 collection, with a micro-rotor automatic movement and a barrel designed to deliver more even power. The ASB19 has a 72-hour reserve, and the stop-work and declutch are what separate it from a conventional automatic. Before you book a service or buy one, check that the shop understands those two mechanisms, since a general automatic specialist may not know them well.
A mainspring does not deliver the same force through its whole unwinding cycle, and a watch's rate can be affected as the spring runs down. Armin Strom's answer was to stop the spring from reaching its weakest range. The Gravity Equal Force was introduced in November 2019 as the first watch in the System 78 collection, and the brand describes the result as more stable torque to the regulating system rather than a guarantee of identical force.
The idea is simple to state and harder to build. The watch needs a barrel that limits how far the mainspring can unwind, and an automatic winding system that can keep working once that limit is reached. The two parts have to be designed together, or the rotor will try to wind a spring that is already at its limit. Armin Strom's engineering is in that combination, and it is worth understanding before you ask anyone to service it.
For an owner, the practical question is whether the watch runs as designed. A service that restores the stop-work and declutch to their correct setting is part of getting the most from the mechanism, and it is a job that deserves a clear plan rather than a quick look.
The stop-work is a Geneva-wheel mechanism that limits the mainspring's operation to a fixed number of turns out of its total range. The brand's technical material gives the working range as nine turns out of a possible twelve and a half, which is the part of the spring it considers more consistent. The declutch sits at the upper limit and allows the rotor to slip, so automatic winding can continue without forcing the locked stop-work.
The barrel arrangement is unusual. The barrel housing turns during winding, while the central arbor drives the going train, which reverses the normal layout. Armin Strom describes the benefit as a more stable, lower-friction drive. A small indicator on the barrel shows the remaining power reserve, and that indicator should move in a way that matches the watch's running.
These parts are small, and their setting matters. A watchmaker should check the stop-work engagement, the declutch slip and the barrel's end play after reassembly. A quote that treats the barrel as a standard part, without checking how it is set, is not a complete service on this watch.
The ASB19 is an in-house automatic with a dial-side micro-rotor. It runs at 3.5 Hz, or 25,200 vibrations per hour, has 202 components and 28 jewels, and gives a power reserve of 72 hours. The watch in the brand's technical material is 41 mm across and 12.65 mm thick, and it is rated to 30 metres. Those figures help you judge whether a shop has the right fixtures and whether the case work matches the watch.
The brand's owner's guides recommend maintenance every three to five years, through Armin Strom or an authorized retailer. The published terms warn that third-party warranty work can invalidate a claim, so a watch still under warranty should go to the brand or an authorized center. Contact the Biel concierge first, and ask for the post-repair warranty in writing, since the brand's published material does not state one for servicing.
Water-resistance testing should follow any case opening, and the owner's guides suggest a test every two years and whenever the case is opened. Ask the shop to record the result, and to replace the gaskets during the work rather than reusing old ones.
Start with the papers. The warranty card should be dated, stamped and signed, and the reference and serial number should match the watch. Check the watch against the specifications for its reference, including the case size and the water rating, because the System 78 collection has several versions with different finishes and cases.
Ask the seller to show the reserve indicator and the automatic winding in action. The indicator should move in step with the watch running, and the rotor should wind the spring without a rough or irregular feel. If the seller can't demonstrate either, ask why before you go further.
Look at the case, crown and caseback. Marks on the caseback edge can suggest an opening by someone without the right tools. Ask whether the watch has been serviced by the brand or an authorized center, and ask for a service record. An independent inspection of the movement, with a report that covers the barrel and stop-work, is the strongest protection before you pay.
A shop that has worked on barrels with stop-work mechanisms or on other movements with a non-standard winding system is a good starting point. Ask whether it has serviced a watch with a declutch or a barrel that turns during winding, and how it checks the setting after reassembly. Ask to see a photograph or a short video of the mechanism on the bench if you're unsure.
For parts, ask whether the shop can source a barrel, stop-work component or declutch part for this reference, and what the lead time is. If a part is no longer available, ask what the alternatives are and what they would change in the watch's running.
Ask for a written estimate that separates the movement, the case and the water-resistance work. Keep the case and crystal decisions separate from the movement, so you can approve each item on its merits.
The ASB19 movement has a 72-hour reserve. The stop-work limits the mainspring to the more even part of its range, so the reserve figure is separate from the limit on spring operation.
It lets the automatic rotor keep winding once the stop-work limit is reached, by slipping rather than forcing the locked mechanism. Without it, the rotor would try to wind a spring that is already at its limit.
No. The Gravity Equal Force aims to steady the power supplied to the regulating system, while the Mirrored Force Resonance links two regulating systems so their balances synchronize.
Often, once the watch is out of warranty, if the shop has worked on barrels with stop-work and declutch mechanisms. Ask how it checks the setting after reassembly before booking.
Gravity Equal Force owners use Armin Strom specialists for servicing, authentication and restoration.
Beverly Hills, CA
Appointment-only luxury watch dealer on Wilshire