Armin Strom Gravity Equal Force Ultimate Sapphire Purple

Over the past 14 months we have reviewed a lot of watches from super affordable microbrands all the way up to some of the finest offerings from the most respected Swiss manufactures. One type of watch we haven't had the chance to review yet was a high horology piece from an independent brand. Today that changes as we take a look at the Gravity Equal Force from Armin Strom.

Armin Strom established his own small watch store and workshop in Burgdorf, Switzerland in 1967. Initially Strom focused on watch service and repair and also sold watches from other brands. After establishing his workshop Strom started to experiment with skeletonizing movements from manufactures like ETA. Soon Strom realized this was his true calling in watchmaking and quickly became an expert in being able to remove all unnecessary material from a movement while still keeping it structurally sound and keeping good time.



After decades of honing his skills Armin Strom finally showed off his work at Basel Watch Fair in 1984. The watch world took immediate notice and Strom's services were soon in demand from an international audience. During the 1980s and 90s Strom expanded his workshop and started to develop his own skeleton movements that often required hundreds of hours to complete. Strom focused on manual wound movements so that more of the movement would be visible.

Besides movement skeletonization Strom also became an expert at hand engraving and guilloche work. Even though Strom employed other artisans and watchmakers, the amount of work each watch received from his own hands was a large selling point for the brand. The 1990s also saw Armin Strom being featured in the Guinness Book of World Records for creating the world's smallest hand skeletonized watch.

In the two decades to follow Armin Strom started to create movements for other manufactures, especially highly skeletonized calibers. The 2000s brought forth the trend of larger and bolder watches and Armin Strom followed that trend with some truly stunning pieces. In 2006 Armin Strom decided it was time to retire and looked to leave the brand in very capable hands.



Growing up businessman Serge Michel and watchmaker Claude Greisler would frequent Armin Strom's workshop frequently as boys. Serge's father was a friend and customer of Armin Strom and the boys found Strom's skeletonized movements fascinating. Upon Armin Strom turning 65 he asked Serge Michel if he would be interesting in acquiring his brand since his own two sons had gone off to pursue unrelated professions.

Both Serge and Claude knew the task ahead would be challenging, but were looking forward to developing the manufacture they loved so much as children. Between 2006 and 2009 they worked to make the brand Armin Strom a fully-integrated in-house manufacture. This meant that the brand would be able to produce and manufacture all components necessary for a completed watch under one roof. 2009 was a major milestone for Armin Strom when they released their first in-house caliber the ARM09.

Under this new leadership Armin Strom debuted their first new watch at Baselworld in the One Week Skeleton featuring the newly created caliber ARM09. The One Week Skeleton was a transitional watch which kept the traditional Swiss-German watchmaking heritage of the brand while showcasing a modern approach.



In the years since Armin Strom would go on to develop calibers with such high complications as a tourbillon to demonstrate their watchmaking abilities. Besides skeletonization, Armin Strom would pioneer and development movements that perfected resonance as well as a series in the Gravity Equal Force that would allow for consistent power delivery to the escapement. A model from the later is what we are going to take a closer look at today.

The story of how Serge Michel and Claude Greisler acquired Armin Strom to continue the legacy of the watchmaker they were so fascinated with as children is a touching one. Even more so with the recent passing of Armin Strom on December 5, 2024.

The Gravity Equal Force Ultimate Sapphire Purple is the latest in the Gravity Equal Force collection from Armin Strom. This collection employs a stop-works (Geneva Stop) system that limits the mainspring's unwinding to be consistence during the entirety of the run time of the watch. Traditionally at the beginning and end of a watch's run time there is either too much or too little energy stored in the mainspring and its accuracy isn't near what is seen during the sweet middle time of operation.



Essentially this system stops the main spring from completely unwinding and only allows the optimal middle portion of the power delivery to be used which keeps constant power delivered to the escapement and keeps the watch's accuracy consistent. Furthermore Armin Strom also added a declutching mechanism built into the mainspring barrel that allows the winding mechanism to slip when the ideal winding state has been reached, which not only prevents overwinding but also keeps optimal torque.

The first thing I noticed about the Gravity Equal Force Ultimate Sapphire Purple was its namesake purple dial. The dial is actually crafted by master artisans Comblemine S.A. which is Kari Voutilainen's atelier. The dial is handcrafted and hand finished using a rose engine lathe. The purple color is applied via a 3D PVD application. The hand guilloche dial can change in color depending on the lighting as well as the angle the watch is situated at. In my experience wearing the Gravity Equal Force I saw colors ranging from red, to pink, to purple and even to light blue. It slightly reminds me of a Ford Mustang Cobra I had in the mid 2000s that would shift paint colors from purple to blue to green. It's a very interesting effect that really needs to be seen in person to be appreciated.

The next thing that caught my attention was how much movement there is when winding the watch. Typically winding is a pretty boring task but with the Gravity Equal Force you tend to see both the micro rotor at one o'clock as well as the main barrel at 5 o'clock turn as the watch is being wound. Being experts at skeletonization the dial also exposes much of the gear train and is just a pleasure to look at. Getting to see so much movement on the dial when winding is just a little extra treat.



Finally the last of my initial time with the Gravity Equal Force Ultimate Sapphire Purple was spent looking at its incredible movement through the sapphire caseback. When you look at articles about the Gravity Equal Force you hardly ever see pictures of the back of the watch with most of the attention paid the brilliant dial. Just like the dial, the movement is also completely hand finished. Cotes de Geneve is widely used on the main bridge and really dominates the view. There is also nice use of perlage, black polishing and anglage showing off sharp inner angles. Finally there is extensive use of engraving to detail the movement's characteristics. The finishing here is just stunning and really couldn't be duplicated by machines.

Now that we have gone over my initial thoughts of the Armin Strom Gravity Equal Force Ultimate Sapphire Purple let's take some time to talk about the technical specifications of the watch. The Gravity Equal Force has a case diameter of 41 mm and a lug to lug length of 48.3 mm. The watch weighs in at 86 grams on the leather strap with a deployant clasp and at its thickest point is 12.2 mm thick. I was a bit surprised that being crafted out of stainless steel the watch was as lightweight as it was. I guess a lot of that has to do with how much sapphire is used in the construction of the watch and the skeletonized nature of the movement. I'd also imagine having a micro rotor over a full sized rotor saved a bit of weight.

Armin Strom uses a flat sapphire crystal with anti-reflective coating on both sides on the Gravity Equal Force. Under the crystal clear sapphire is a masterclass of dial hand finishing as well as movement technology and skeletonization. As previously discussed the Kari Voutilainen hand guilloche dial with purple PVD treatment differentiates this Gravity Equal Force from previous models. The craftsmanship of the dial is just mind-blowing to me and up there with the best I have seen in person. The added bonus of the dials ability to shift colors in the light is really the chef's kiss.



The time telling duties are taken care of by offset dials on the left hand side of the dial. This is the largest subdial on the watch with a transparent crystal and a printed minute track and Arabic numerals. The Armin Strom branding is also printed on this subdial. Underneath you can clearly see the exposed gear train of the movement. The polished hour and minute hands are coated with a healthy amount of Super-Luminova that glow a bright green in low light. Also of note, these are the only lumed elements on the dial.

Situated between 6 and 9 o'clock on this subdial there is another more opaque crystal subdial which contains the small running seconds hand. Like the hour and minute hands the seconds hand is also polished, but it does not contain any lume. The sub-seconds subdial being more opaque than the main time subdial also provides a nice contrast on the dial.

The right hand side of the dial is dominated by three large finger style bridges that are connected to the micro rotor at 1 o'clock and the main barrel at 5 o'clock. These bridges are hand finished and polished and just look spectacular. The winding rotor is nice and thick as you can see from the negative space left from the portion not covered by the rotor. The housing of the rotor is also finished with some stunning perlage.



The cover to the main spring is engraved with "Equal Force" and contains I nice added complication I missed at first glance. There is a small power reserve indicator displayed on the cover which is very subtle since it's done in the same color as the cover. All the magic happens under this cover where the stop-work and declutching mechanisms reside. It's nice to know at lot more than meets the eye is going on under the mainspring cover.

With how much depth there is on the dial of the Gravity Equal Force is goes without saying that the rehaut is rather tall. There is a decent amount of space between the top of the crystal and bottom of the purple dial. Throughout this negative space you can see the bridges, main barrel, time subdial and winding rotor. Visually this depth is one of my favorite things about the watch.

The case of the Armin Strom Gravity Equal Force is crafted out of stainless steel and features a mixture of brushed and polished surfaces. The bezel area is done in a high polish as are the chamfers on the lugs. The mid case and flat areas of the lugs are done in a brushed finish. This contrast of finishes really lets the watch straddle the line between dress and sports watch.



The right hand side of the case contains the non-screw down crown which is mostly satin in appearance. The crown has some very nice scalloping to it and provides ample grip. The top of the crown is complete with an engraving of the Armin Strom logo. In the resting position the crown allows for manual winding of the automatic movement. Being a time only watch there is only one position to the crown. When pulled out to position one the time is allowed to be set and the sub-seconds hand stops to allow precise time setting. As expected with a watch of this caliber, there is no jump in the minute hand when the crown is pushed back in. With the non-screw down crown the Gravity Equal Force has a water resistance of 30 meters, more than enough for a splash of water but not really recommended for aquatic activities.

Flipping the watch over shows off the large display caseback covered with a sapphire crystal. The bezel of the caseback is extreme slim and allows for so much more of the movement to be put on display. Since so much of the case back is covered by sapphire, a lot of the details about the watch are engraved into the movement itself. We already spoke about the fine hand finishing previously but it really is expertly done. It's also nice seeing the back of the large main barrel from the caseback. There is a matching finger bridge found on the back of the movement that holds the beating balance as well.

The Armin Strom Gravity Equal Force is powered by the in-house caliber ASB19. The movement is automatic and features a dial side micro rotor which feeds the mainspring. The movement beats at 25,200 vph (3.5Hz) and has a power reserve of 72 hours. Note that the power reserve is actually longer than 72 hours, but 72 hours is the time the watch is able to retain consistent power to the escapement and allowed to run. On our timegrapher the Gravity Equal Force had an accuracy of +1 seconds when averaged out over several positions. Even more important the timegrapher showed zero beat error from the movement.



The Gravity Equal Force has a lug width of 20 mm and comes on a grey leather strap. The strap tapers down to 18 mm at the brushed and polished deployant clasp. The flat area of the clasp features the Armin Strom logo and is brushed in finish. The sides of the clasp are polished and feature the two pushers to release the clasp. The top of the strap features grey suede complete with purple stitching on both sides. The back of the strap is textured and is done in the same purple hue as the dial. I really loved this strap and not only thought it looked amazing and suited the watch perfectly, but it was also very comfortable.

The Armin Strom Gravity Equal Force arrived at an interesting time when we were very low on watches in for review so I had a good amount of time to spend with the watch. As I'm writing this review we have eight watches currently in transit to us, so having such an opening to focus on a review watch is pretty rare. During this time I really tried to wear the Gravity Equal Force as my sole watch. Also I haven't bought a personal watch in months and my recently repaired watches have become less novel since they've been home for a while now.

If you have read many of my reviews you can tell that I'm not a huge fan of stainless steel watch cases. This typically comes down the added heft they add, especially with my preferred over 50 mm lug to lug length. The Gravity Equal Force doesn't really have weight any penalty added for it being crafted in stainless since so much of the case is done in sapphire and the movement is skeletonized. At only 86 grams on our scale it actually weights a good deal less than a lot of ceramic, titanium and carbon watches we've had in recently. This translated to the watch completely disappearing on wrist when being worn and giving me zero wrist fatigue.



The watch is a good deal smaller than my personal target of 50 mm lug to lug, but honestly I didn't notice that when I was wearing it and the smaller lug to lug only became known when doing research for this review and measuring it with our calibers. The excellent leather strap not only looked amazing but it also was extremely comfortable and kept the watch centered on my wrist. With watches smaller than 50 mm I can't stand when the watch favors one side of my wrist over the other. I have a fairly flat 7.25 inch wrist with a flat area of 55 mm, so I can wear larger watches just fine and smaller watches can also look a bit asymmetrical if they don't sit centered.

Since the Gravity Equal Force is meant to be more of a showcase of the skeletonizing and technical expertise Armin Strom has achieved, legibility really wasn't at the forefront of its design. In reality for collectors watches don't really have to be all that great at displaying time, the real draw is the mechanics or design behind the piece. The way I test a watch's legibility is to see how hard it is to tell the time on a watch while driving at a glance. Even with all the skeletonization the large time telling subdial is pretty easy to decipher at a glance. Now I wouldn't rate it as legible as a large diver with high contrast oversized numerals and hands, but it was more than easy enough to tell the time at a glance.



I had a strong feeling that the Armin Strom Gravity Equal Force Ultimate Sapphire Purple would attract a lot of attention when being worn out… and I was right. The combination of the stunning bright purple skeletonized dial and awesome grey and purple strap are a perfect recipe for getting glances. I had a few people come up to me and ask about the watch and also showed the watch to a few friends of mine when out of dinner and drinks. Everything said about the watch was positive with most people really being most fascinated with the exposed gears and movement. If I was in an area with good lighting I could also show off the color changing effect of the purple hand guilloche dial, which also really impressed those who saw it. The price did give pause to most people I disclosed it to, but in all honesty anything more expensive than a Rolex Submariner is pushing it to watch lay-people.

Speaking of price the Gravity Equal Force Ultimate Sapphire Purple retails at just over $28,000. For that price you are getting a completely unique watch with both a hand finished dial and movement. On top of that the dial is finished by non-other than Kari Voutilainen. Past that you are also getting an in-house movement with an extremely rare dial side micro rotor and groundbreaking stop-work and declutching mechanisms that retain consistence power to the escapement. It would now be a great time to look at other watches that offer similar features and see how the value of the Gravity Equal Force stacks up.



Up first we have the Tradition 7057 from Breguet which is crafted out of white gold and has a case diameter of 40 mm. The Tradition like the Gravity Equal Force shows a lot of the movements workings dial side and uses a smaller sub-dial to display the time. There is also a subtle power reserve indicator at 10 o'clock. The Tradition has a similar 30 meter water resistance and is powered by a manual winding in-house calibre 507 DR1 with 50 hours of power reserve which is a bit less than the Armin Strom. The Tradition is also a good bit more expensive at $33,300.

Moving on we have the Neo Constant Escapement from Girard-Perregaux which is a 45 mm watch crafted out of titanium. Like the Gravity Equal Force and Tradition, the Neo Constant Escapement displays a lot of the movement dial side including the constant force escapement. Like the Gravity Equal Force, the Neo Constant Escapement delivers consistent energy no matter what the amount of power left in the main spring is. Like the other two watches the Neo Constant Escapement offers 30 meters of water resistance. It is powered by an in-house caliber GP09200 which is hand wound and has at least seven days of power reserve which is a lot more than the Armin Strom and Breguet. The Neo Constant Escapement also comes in at a lot more than the Gravity Equal Force at $99,600.



Next up is the Zeitwerk Date from A. Lange & Sohne which is crafted out of white gold and has a case diameter of 44.2 mm. The Zeitwerk Date is more of a traditional looking watch with the main calling card being its big hour and big minute displays. Like the other watches the Zeitwerk Date offers 30 meters of water resistance. The watch is powered by an in-house manually wound caliber L043.8 which offers 72 hours of power reserve. Like the Armin Strom and Girard-Perregaux, the Zeitwerk also uses a constant force mechanism that keeps energy consistent through the watch's power reserve. The Zeitwerk Date is also much more expensive than the Gravity Equal Force with an estimated retail price of around $130,000.

Finally we have an oddball from IWC in the Tribute to Pallweber Edition 150 Years which is crafted out of stainless steel and has a case diameter of 45 mm. The main feature of this watch is its jump hour and minute display which are powered by a separate mainspring than the mainspring that powers time keeping duties. This allows for the watch to be more accurate and not lose power and consistency by powering both time keeping and complications by the same mainspring. The watch once again has 30 meters of water resistance. It is powered by an in-house hand wound caliber 94200 with 60 hours of power reserve. The Tribute to Pallweber Edition 150 Years has been out of production for a few years but had a retail price in 2019 of 24,000 Euros.



As you can tell from the above four watches when adding a mechanism to a movement to improve power distribution the price of the watch goes up quickly. Price wise the Gravity Equal Force is closest to the IWC and Breguet but honestly offers a much more technical solution to consistent power delivery. The watches from Girard-Perregaux and A. Lange & Sohne offer a similarly complex solution to power distribution but both cost many times more than the Gravity Equal Force. By looking at these watches the Armin Strom excels by providing an exotic and stunning hand-finished skeleton dial with an advanced method of delivering power for the least amount of money. That shows great value in my opinion.

So in the end is the Armin Strom Gravity Equal Force Ultimate Sapphire Purple for me? Typically I'm much more into sportier watches and divers. Even my pilot's watches are crafted out of black ceramic and don't look very traditional. With that being said I only have titanium, ceramic and carbon watches in my personal collection of timepieces. Also all of my personal watches are right at or just over 50 mm of lug to lug length. So with all that, you would think that the watch really isn't for me then…



In truth I really do feel like the Gravity Equal Force would be a great watch to add to my collection. I don't really have any personal watches that are fully or partially skeletonized. Also even though the watch is crafted out of stainless steel it manages to keep a very low weight by using so much sapphire in its construction. While the watch is a decent bit shorter lug to lug than 50 mm, it does look really good on my wrist and never favors one side over the other. The hand guilloche dial in its purple finish is just beyond spectacular as well. Pairing that with an equally impressive hand finished movement is a massive bonus.

The aesthetics of the watch with its suede grey leather strap with purple stitching also complimented my dress of mainly black t-shirts, shorts and sneakers perfectly as well. Sure the watch can be worn as a dressier piece, but it also goes perfectly with a casual look. The technology developed by Armin Strom to achieve constant power delivery is something I love knowing is working under the visible main barrel cover as well. Plus I'm just a sucker for a micro rotor, even better one that is visible dial side.



It shouldn't be a surprise then that I would fully recommend the Armin Strom Gravity Equal Force to anyone looking for an expertly finished watch with an interesting take on movement accuracy and consistency. The story of how the current owners of the brand took over the business from their childhood watchmaking hero upon his retirement is just one of the great stories found throughout the history of watchmaking.

I'd really like to thank Armin Strom for sending us this Gravity Equal Force Ultimate Sapphire Purple. The watch served as a great introduction to the brand and shows some of the soul independent watches possess over their large watch group counterparts. In the near future it would be amazing if we were able to review a watch from Armin Strom's resonance series to see how they incorporated resonance into their movements.



For more information about the Gravity Equal Force please visit : Armin Strom

Technical Specifications

Reference Number: ST24-GEF.SA

Retail Price: CHF 25'439

Case Size: 41 mm

Lug to Lug: 48.3 mm

Thickness: 12.2 mm

Weight: 86 Grams

Case Material: Stainless Steel

Bezel: Stainless Steel

Strap: Grey Leather Strap with Stainless Steel Deployant Clasp

Movement: In-House ASB19 Automatic Movement

Functions: Hours, Minutes, Seconds, Power Reserve, Equal Force

Power Reserve: 72 Hours

Water Resistance: 30 Meters