Explained: Barrels, Mainsprings, and the Trade-off Between Power Reserve and Energy

Parallel vs. in-sequence.

Every mechanical watch employs at least one mainspring barrel as its energy source. When a watch is wound, the coils of the mainspring tighten, storing potential energy which is then slowly released through the gear train to the escapement.

The mainspring is enclosed in a toothed barrel, essentially a drum covered by gear teeth. As a result the barrel is often considered to be the first wheel of the going train. 

Although one is the norm, two or even more barrels can be employed, typically to generate more energy. Double barrel movements usually feature two mainsprings kinematically linked in one of two ways: in parallel or in series. The number of mainsprings, energy stored, and power reserve are illustrated with equations (1), (2), and (3):

As described by equation (1), the energy of a single barrel E is a function of its torque, angular discharge velocity and running time (autonomy).

Linking two identical barrels naturally means having twice the energy, so 2E. By convenient association, equation (2) exploits the available energy to double the torque sent to the gear train, while equation (3) takes advantage of the total energy by doubling the running time. 

Parallel barrels

The parallel arrangement of barrels embodies equation (2), which delivers twice the torque, increasing the energy available to run the movement (but not increasing the running time).

Here two barrels unwind at the same time on a centre pinion connected to a second mobile of the going train. An embodiment of the parallel linkage is illustrated in fig. 1.

Fig. 1 – Outline of a parallel linkage between two barrels

The two mainspring barrels (yellow) act on the centre pinion (purple). The mainsprings (black) are each connected each to an arbour and ratchet wheel (green). The two ratchets are connected by a crown wheel (red), itself linked to a winding system (not depicted).

In this set up, identical barrels are wound at the same time and at the same rate, and then discharge their energies simultaneously. The two barrels have the same developing speed and running time, but their torques cumulatively add up in turning the centre pinion. The equal pressures exerted by the two barrels from opposite sides on the pinion tend to cancel out, contributing to the parts’ longevity. 

The utility of the parallel setup lies in the fact that the power transmitted to the balance is much greater than in a single-barrel movement, which greatly improves chronometry. Consequently, many vintage and modern precision timepieces rely on two barrels unwinding in parallel, ranging from 19th century Breguet pocket watches to contemporary F.P. Journe wristwatches like the Chronometre Optimum.

Two barrels working in parallel are also useful for a watch that features a particularly power-intensive complication – like the MB&F LM Thunderdome. The Thunderdome needs not two, but three, barrels coupled in parallel to deliver the necessary energy to power the fast revolving, multi-axis tourbillon.

Barrels in series

Equation (3) that delivers increased power reserve is associated with barrels arranged in series. Two barrels working serially (or in sequence) deliver torque equivalent to just one barrel at any point in time, but as they unwind one after another, the respective running times add up for longer autonomy overall.

Fig. 2 – Outline of a series linkage between two barrels

The basics of serially-coupled barrels can be observed in fig. 2. A crown wheel (red) engages with the ratchet wheel (green) of the first barrel (yellow). The two barrels are geared directly to each other by their toothed drums.

The mainspring in the second barrel is linked by an arbour to its ratchet wheel (green) that is larger in diameter than the barrel. This oversized ratchet wheel connects to the centre pinion (purple).

When the watch is wound through the dedicated system, the first mainspring (black) winds up and turns its barrel wall, followed by the second mainspring winding up via the geared drum. The energy is discharged via the second barrel’s arbour, through the oversized green gear to the going train via the centre pinion.

In short, the barrels are wound one after another when the movement is being wound, and then the barrels unwind one after another when the movement is running.

The two mainsprings’ respective numbers of developing turns are cumulative. They unwind at the same rate, but one after another, meaning their respective discharge times are also cumulative. As a result, the running time of the watch is doubled, even though the torque delivered to the gear train is at any given moment equivalent to a single barrel’s output.

Such series coupling is mostly used in long power reserve movements, for example the IWC 52000 family with a seven-day power reserve, or at the extreme, the Hublot MP-07 with its nine barrels and a 40-day power reserve.

The Hublot MP-07 with nine barrels arranged concentrically across the diameter of the case

A single large barrel can also lengthen a watch’s power reserve, but it would affect timekeeping due to fluctuating torque reaching the regulating organ.

Any sort of mainspring delivers high torque when fully wound, then settles for a median value for most of its running time, before dropping off as it is nearly empty. These variations in torque are more pronounced for big barrels.

A timepiece with a long power reserve (say more than three days) running on a single large barrel would probably run fast for the first day, reasonably well for the next two to three days, then experience a severe drop in rate.

One solution is a constant-force mechanism to even out the uneven torque, as used in the Lange 31 which employs two enormous mainsprings for a one month’s worth of power reserve.

The Lange 31 features two huge barrels stacked one on top of the other, each containing a mainspring over 1.8 m long

Sequenced barrels, on the other hand, exhibit a much flatter torque curve over the course of their running time, and perform more consistently than each of the individual barrels operating separately.

As a result, some movements utilise smaller barrels coupled in series. Here the goal is not to extend the power reserve, but employ smaller or shorter mainsprings with less energy output. Sequential smaller barrels work at higher revolving speeds but deliver lower and more consistent torque than a single mainspring with an equivalent power reserve.

The Omega cal. 8912 with its helpfully labelled barrels “One” and “Two”

This approach is thought to increase a movement’s longevity, as the strain on the going train is smaller. The Longines L.990 and most last generation Omega co-axial movements make use of this principle in their construction.


 

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Audemars Piguet Introduces the Code 11.59 in Pink Gold

More options and 38 mm cases.

To mark the collection’s fifth anniversary, Audemars Piguet (AP) has launched seven new variants of the Code 11.59 in pink gold that are available in both 41 mm and 38 mm cases, with the 41 mm option being available with or without a chronograph.

While none of the individual elements are novel (the new models are a melange of successful elements from recent launches) the new 38 mm model in navy blue – specifically the same hue as the Royal Oak “Jumbo” ref. 5402 ST – is one of the most appealing variants of the Code 11.59 to-date.

Initial thoughts

Though often considered a gateway to the brand’s most sought-after models like the Royal Oak, the Code 11.59 has quietly evolved into a full-fledged collection that now includes everything from simple time-only pieces to the grandest of grand complications. 

The new references reflect the updated Code 11.59 aesthetic introduced last year in stainless steel, which comprised an updated hand set and stamped guilloché dials in crowd-pleasing colours like navy blue and dark green.

It is in this respect that the 38 mm model with navy blue dial that stands out. While not the first 38 mm Code 11.59, it is the first in a mainstream colourway. Combined with the more wearable size, this new variant adds significant appeal to the overall collection.

The pricing of the new Code 11.59 depends on the size and the complication: the 38 mm models are priced at CHF27,500, while the 41 mm is available for extra CHF1,000 and the chronographs all priced at CHF40,000. It is slightly lower than alternatives like the Patek Philippe ref. 5226G, which offers its own take on the contemporary dress watch format, including a signature hobnail case band.

Finding the sweet spot

In the five years since the launch of the Code 11.59, more than 80 references have been introduced. Despite the proliferation of options, many have been niche products ranging from a minute repeater and grande sonnerie to a variety of flying tourbillon models. Even among the simpler models, many have been introduced in unusual colours like purple and ivory.

Things finally started to change last year when the stainless steel collection was introduced, targeting more mainstream tastes and budgets. Continuing this trend, the new 38 mm (ref. 77410OR.OO.A342CR.01) is arguably the most appealing variant to-date.

The 38 mm size might be the sweet spot for the Code 11.59 case, which wears large thanks to its narrow bezel and large dial. The rose gold case features the collection’s signature octagonal case band.

The coup de grâce is the combination of these elements with a patterned dial in what Audemars Piguet calls “Bleu Nuit Nuage 50”, or navy blue, the shade replicating the colour found on the original 1972 Royal Oak and also applied to the modern-day Royal Oak “Jumbo” ref. 16202.

Like most recent Code 11.59 models, the dials of the new additions are guilloché. While the brand endured criticism for the use of stamped dials in the past, it’s important to note that the pattern itself is novel, and not conducive to traditional methods of guilloché.

Overall, these seven new references bring the Code 11.59 closer to the mainstream, which is a good thing. For the collection to have long-term staying power, it will need to evolve beyond its current reputation as a stepping stone and into something that is appealing on its own merits.

Full-featured movements

As expected, the new references are powered by the brand’s latest generation movements. The 41 mm variants in time-only and chronograph formats are powered by the cals. 4302 and 4401, respectively, while the 38 mm options are powered by the cal. 5900.

All three movements bear the hallmarks of modern construction, namely a 4 hz rate, a free-sprung balance suspended by a full balance bridge, and above-average power reserves. That said, it’s worth noting that the cal. 5900 is produced by Vaucher, as evidenced by the distinctive form of the balance bridge.

The cal. 4401

As is typical for AP’s mainline products, all three movements are machine-finished to a high standard and feature a few clearly hand-finished details, like inward angles on the rotors, that elevate the overall appearance.


Key facts and price

Audemars Piguet Code 11.59 38 mm
Ref. 77410OR.OO.A344CR.01 (light blue)
Ref. 77410OR.OO.A342CR.01 (navy blue)

Diameter: 38 mm
Height: 9.6 mm
Material: 18k rose gold
Crystal: Sapphire
Water resistance: 30 m

Movement: Cal. 5900
Features: Hours, minutes, seconds, and date
Frequency:  28,800 beats per hour (4 Hz)
Winding: Automatic
Power reserve: 60 hours

Strap: Alligator with pin buckle

Limited edition: No
Availability:
At AP Houses and boutiques
Price: CHF27,500


Audemars Piguet Code 11.59 41 mm
Ref. 15210OR.OO.A348KB.01 (navy blue)
Ref. 15210OR.OO.A056KB.01 (green)

Diameter: 41 mm
Height: 10.7 mm
Material: 18k rose gold
Crystal: Sapphire
Water resistance: 30 m

Movement: Cal. 4302
Features: Hours, minutes, seconds and date
Frequency: 28,800 beats per hour (4 Hz)
Winding: Automatic
Power reserve: 70 hours

Strap: Alligator with pin buckle

Limited edition: No
Availability:
At AP Houses and boutiques
Price: CHF28,500


Audemars Piguet Code 11.59 Chronograph
Ref. 26393OR.OO.A348KB.01 (navy blue)
Ref. 26393OR.OO.A056KB.01 (green)
Ref. 26393OR.OO.A056KB.01 (black)

Diameter: 41 mm
Height: 12.6 mm
Material: 18k rose gold
Crystal: Sapphire
Water resistance: 30 m

Movement: Cal. 4401
Features: Hours, minutes, sub-seconds, chronograph, and date
Frequency:  28,800 beats per hour (4 Hz)
Winding: Automatic
Power reserve: 70 hours

Strap: Alligator with pin buckle

Limited edition: No
Availability:
At AP Houses and boutiques
Price: CHF40,000

For more, visit Audemarspiguet.com.


 

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Audemars Piguet Introduces the Royal Oak Tourbillon Openworked “Sand Gold”

A new shade for a familiar gold alloy.

Audemars Piguet (AP) has introduced the Royal Oak Selfwinding Flying Tourbillon Openworked in a new proprietary 18ak gold alloy known as sand gold. Essentially a precious-metal variant of the steel version released in 2022, the new Tourbillon Openworked showcases the brand’s commitment to interesting materials – possible in part due to AP owning its own case maker.

While the hype for integrated-bracelet sport watches has ebbed, AP has continued to deliver successive variants of its popular Royal Oak in exotic materials ranging from brown ceramic to frosted gold. Priced at CHF250,000, this latest variant pairs a warm-hued gold case and bracelet with one of the brand’s most modern movements.

Initial thoughts

Unlike its “Holy Trinity” peers Patek Philippe and Vacheron Constantin, Audemars Piguet has firmly embraced a contemporary, architectural aesthetic throughout its collections. The new Tourbillon Openworked is emblematic of this theme, eschewing traditional decorative finishes like Côtes de Geneve in favour of minimalist graining and sharp angles.

Featuring the brand’s latest generation flying tourbillon movement plated to match the case, the sand gold tourbillon presents a striking monochrome appearance. While skeletonised watches can often look fussy and chaotic, the geometric bridges of the cal. 2972 were clearly designed with openworking in mind. As a result, the overall aesthetic is clean and organised.

The 41 mm case is well-proportioned at just 10.6 mm in thickness, which is thinner than many simple sport watches despite its automatic flying tourbillon movement. And while the sand gold alloy is new, the finishing is done in typical Royal Oak fashion, straight-grained with polished bevels.

Sand gold

The core novelty of the Tourbillon Openworked is clearly its sand gold case and bracelet. Similar to A. Lange & Söhne’s proprietary Honey Gold, sand gold presents as something between white gold and rose gold, but appears darker; it’s hard to be more specific judging by the stock images alone. Interestingly, the alloy is resistant to fading over time, something that often happens with rose gold, especially if exposed to chlorine or salt water.

Only a handful of brands, including Rolex, Omega, Hublot, and now Audemars Piguet, have developed proprietary rose gold (or rose gold-adjacent) alloys with permanent characteristics. This is achieved by mixing certain stable metals, palladium in this instance, with the copper typically used to create rose gold.

Purpose-built skeleton

The Tourbillon Openworked is powered by the cal. 2972, which made its debut in 2022. The movement was engineered from the ground up as a skeletonised caliber, as evidenced by the neat and tidy bridge layout.

One of the distinctive characteristics of this movement is the fact that the motion works has been relocated to the upper half of the dial, enhancing the visual spectacle of the tourbillon. And it doesn’t just look good; the motion works features anti-backlash gearing to enhance the experience of setting the time.

In this application, the bridges of the cal. 2972 have received a galvanic treatment giving it a similar hue as the case, creating a sense of continuity that befits the overall design.


Key facts and price

Audemars Piguet Royal Oak Selfwinding Flying Tourbillon Openworked “Sand Gold”
Ref. 26735SG.OO.1320SG.01

Diameter: 41 mm
Height: 10.6 mm
Material: 18k sand gold
Crystal: Sapphire
Water resistance: 50 m

Movement: Cal. 2972
Features: Hours, minutes, and 60-second tourbillon
Frequency:  21,600 beats per hour (3 Hz)
Winding: Automatic
Power reserve: 65 hours

Strap: 18k sand gold bracelet

Limited edition: No
Availability: 
At AP Houses and boutiques
Price: CHF250,000

For more, visit audemarspiguet.com.


 

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Audemars Piguet Debuts a Royal Oak Pair with Smoked Yellow Gold Dials

A striking gold-on-gold livery.

Audemars Piguet has just launched its “first semester collection” that’ll take us through the first half of the year. Most are variations of current models, with two of the most striking sharing the same dial in “smoked yellow gold”, namely the Royal Oak Frosted Gold Selfwinding 37 mm (ref. 15550BA) and the Royal Oak Selfwinding Chronograph 41 mm (ref. 26240BA). Both are fashioned in yellow gold and complemented by a striking dial with a gradient yellow gold finish, conceived to homage to the brand’s yellow gold Royal Oak models of the 1970s.

Initial thoughts

The smoked yellow gold finish was introduced on the Royal Oak “Jumbo” in 2022, so the new releases aren’t a surprise. Nonetheless, it is satisfying to see this dial finish on more compact models like the 37 mm ref. 15550.

Between the two releases, the time-only ref. 15550 is the standout. The clean, radially brushed dial pairs perfectly with the finely grained texture of the frosted case. On the other hand, the dial finish is less punchy on the chronograph due to the traditional tapisserie guilloche. The chronograph, however, is an imposing watch overall due to its size and weight.

The time-only model retails for CHF55,000, while the chronograph is priced at CHF63,000 – both sit in the current range for similar Royal Oak models. Neither is a value proposition, though both are appealing variants of the design.

Smoked yellow gold dials

Both new launches are variants of existing models, compact Royal Oak ref. 15550 and the Royal Oak flyback chronograph ref. 26240.  The brand asserts the all-yellowgold aesthetic is inspired by 1970s Royal Oak models in the same alloy.

The distinguishing feature of both is the smoked finish on the dial that goes from yellow gold to black on the edges. It was achieved with hand-applied varnish. To contrast with the yellow gold finish, both sport a black rhodium-plated 24k gold logo applied just below 12. 

While both have the same dial colour, the two are quite different, size and complication aside.

Measuring 37 mm in diameter and 9.1 mm high, the ref. 15550BA is minimalist for a Royal Oak with a dial that does away with usual tapisserie guilloche. The 18k yellow case has a “frosted” finish attained by employing a diamond-tipped graver to create tiny divots in the gold, creating a granular, sparkly finish.

Due to its small size, the ref. 15550BA employs the cal. 5900, an automatic movement made Vaucher that features a full balance bridge and a power reserve of 60 hours.

The cal. 5900

On the other hand, the chronograph ref. 26240BA retains the traditional chequerboard pattern on the dial. It has gold-tone sub-dials with black numerals matched with white print for the seconds scale. Here the dial is paired with a traditionally finished case that has brushed surfaces and polished edges.

It is also a large watch at 41 mm wide and 12.4 mm high – the largest diameter case for a Royal Oak chronograph that isn’t an Offshore. It is driven by the cal. 4401, an integrated movement featuring a column wheel and vertical clutch. Equipped with a flyback mechanism, the chronograph allows for instantly resetting and restarting.


Key facts and price

Audemars Piguet Royal Oak Frosted Gold Selfwinding 37 mm
Ref. 15550BA.GG.1356BA.01

Diameter: 37 mm
Height: 9.1 mm
Material: Hammered 18k yellow gold
Crystal: Sapphire
Water-resistance: 50 m

Movement: Cal. 5900
Functions: Hours, minutes, seconds, and date
Winding: Automatic
Frequency: 28,800 beats per hour (4 Hz)
Power reserve: 60 hours

Strap: Matching bracelet with folding clasp

Limited edition: No
Availability:
At AP Houses and boutiques
Price: CHF55,000


Key facts and price

Audemars Piguet Royal Oak Selfwinding Chronograph 41 mm
Ref. 26240BA.OO.1320BA.02

Diameter: 41 mm
Height: 12.4 mm
Material: 18k yellow gold
Crystal: Sapphire
Water-resistance: 50 m

Movement: Cal. 4401
Functions: Hours, minutes, seconds, date, and flyback chronograph
Winding: Automatic
Frequency: 28,800 beats per hour (4 Hz)
Power reserve: 70 hours

Strap: Matching bracelet with folding clasp

Limited edition: No
Availability:
At AP Houses and boutiques
Price: CHF63,000

For more, visit Audemarspiguet.com.


 

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