The Jaeger LeCoultre Master Ultrathin

The Jaeger-LeCoultre Master Ultrathin

by ei8htohms
© 2-18-2003


Jaeger-LeCoultre is clearly one of the most important manufactures in Swiss watchmaking, responsible for scientific and manufacturing breakthroughs that revolutionized the industry as well as designing and manufacturing movements for the most prestigious houses in Switzerland. Even before the company began manufacturing watches under their own name in 1929, the horological triumphs of Antoine LeCoultre and the LeCoultre & Co. atelier were many and varied. Having invented the Millionometer (the first measuring instrument capable of a resolution of 1/1000th of a millimeter) in 1844 and a keyless winding system in 1847 and creating the world’s thinnest pocket watch movement in 1903 (at only 1.38 mm thick), the company’s legacy was already well established when the holding company of Jaeger-LeCoultre was established in 1925 in conjunction with Edmond Jaeger. The following year saw the release of the revolutionary Duoplan two stage movement and in 1929 the company announced the smallest watch movement ever: the calibre 101 (it remains the world's smallest mechanical movement to this day). Jaeger-LeCoultre has never been one to rest on its laurels and the famous Atmos, Reverso, Futurematic, Memovox and mecha-quartz chronograph are only a few of their other notable horological contributions.

With a supreme talent for miniaturization, it is no surprise that JLC excels in the creation of ultrathin calibres. They created the famous ultrathin manual wind calibre VC 1003/AP 2003 widely used by Vacheron Constantin and Audemars Piguet as well as the ultrathin automatic calibre VC 1120/AP 2120/PP 28-255 which was also used by Patek Philippe. It stands to reason that JLC’s own ultrathin calibre would exhibit their exceptional skill in this most challenging category. Introduced originally as the calibre 839 in 1975, updated and renamed in 1994, the calibre 849 ultrathin manual wind movement is currently available in the Master Ultrathin. The time-honored craft and precision manufacturing of JLC are still readily apparent in the details of the watch’s execution, inside and out. It offers a level of quality that is excellent by any standard but simply astounding given its modest price tag.

The Exterior

The Jaeger-LeCoultre Master Ultrathin featuring the ultrathin cal. 849 manual wind movement is at once contemporary and classic. While quite small relative to the oversized watches that have become commonplace in recent years, at 34 mm in diameter it is sized perfectly for a dress watch. Boasting a thickness of a mere 4.2 mm, it is available in steel, white gold or rose gold (a limited edition in platinum from 2001 also exists).

The gentle curves of the (slightly domed) sapphire crystal, case, dial and hands all add to the look and feel of slender elegance that the watch creates. On the wrist, it goes completely unnoticed by the wearer and only attracts the attention of others for its simplicity and clean design. Lacking even a second hand, it is a distillation of the essential elements of a wristwatch.

Despite its dressy elegance, the Master Ultrathin exhibits a number of functional touches that render it suitable for everyday use as well. For instance, the dauphine hands are half frosted to allow for maximum visibility in a number of lighting situations, something that is especially appreciated in combination with a black dial. Somewhat miraculously for an ultrathin mechanical watch, it is water resistant to 5 atmospheres (3 atmosphere is the modern standard for dress watches), making it more than amply protected from rain or other unexpected soakings.

This astounding level of water resistance is made possible by the masterful case construction [1] that provides a great deal of strength despite its unassuming shape. The sapphire crystal is tightly friction-fit into a nylon gasket and the four screws that secure the bezel through the case band compress the rubber gasket under the bezel securely. In addition, the bezel has two large semi-circular tabs that fit precisely into milled out portions of the caseband for increased rigidity.

The stainless steel version with the black dial is also fitted with a sapphire crystal display back [2] held in place by four screws. All the ruggedness and strength inherent in the case design were somewhat undermined in this example, however, by the drastically under-tightened case and bezel screws [3] that were also oddly unpolished.

The Bridges

The layout of the calibre 849 is eminently appealing, timeless and functional. The four graceful bridges are secured by heat blued screws [4] with delicately beveled heads and chamfered slots. The crown wheel and ratchet wheel are each secured with three small screws and the nicely formed click is held in place by a wire spring that is almost completely hidden under the barrel bridge (the reason any part of it is exposed is a mystery). As is sometimes seen in thin movements, a couple of tall screws act as safety pillars on either side of the balance. If the caseback is flexed or otherwise brought into contact with the movement, these screws will keep it from pressing on the balance bridge and stopping the movement.

The center wheel, third wheel and fourth wheel run in jeweled bearings in a nicely curved bridge. In this example, the anglage of the power train bridge was slightly inconsistent [5], as traditional handwork sometimes is. The escape wheel has its own cock and a Kif cap jewel setting that, combined with the cap jewel on the dial side of the escape wheel, brings the jewel count to 19. The Kif springs on both sides of the escape wheel are simply a convenient way of holding the cap jewels in place as the jewel settings are not shock protected (nor need they be).

All of the holes in the bridges have polished countersinks although not finished to the level of a haute de gamme timepiece [6]. The decorative finishing on all the visible surfaces is similarly very well executed while just short of exquisite. It shows a serious commitment to tradition and craft significantly above what can otherwise be found in this price range.

The Dial Side

With the dial removed, the bottom plate shows off the novel ultrathin construction with its hanging barrel, completely exposed through a large hole in the plate. The hanging barrel employed in the calibre 849 is only supported by the barrel bridge, squeezing a few more fractions of a millimeter out of the thickness of the movement by doing away with the lower barrel arbor pivot and its bearing in the main plate (more on this later).

The keyless works are classic Jaeger-LeCoultre in design and execution [7]. The levers are all straight grained on top with chamfered edges and the functional surfaces and undersides are all smooth if not highly polished. The clutch lever return action is assured by a shaped steel spring, a finer and more expensive solution than the wire springs found in lesser movements. The underside of the set bridge [8] was slightly cruder than the undersides of the clutch lever and return spring [9] both of which had a more consistent matte finish. While a slightly finer finish may be found on JLC keyless levers from the middle of the last century, the overall fineness of design and execution still surpasses anything that can be found in a comparably priced watch today.

The hand-setting and dial train wheels are all nicely made and appropriately lubricated (as were the keyless levers). The plate was perlaged to nice effect although its application was a little inconsistent, allowing minor scratches to show through the circular patterns, which were not arranged perfectly concentrically either. Taken into account with the unpolished countersinks [10] for the jewels and other holes in the bottom plate, the overall impression is still one of high quality artisanship.

The Power Train

After removing the three screws that attach the ratchet wheel to the barrel, one might expect the barrel to simply drop out through the main plate. As it turns out, the diameter of the toothed portion of the barrel drum is larger than the hole in the plate so the barrel rests nicely in the same position after the ratchet wheel is removed. This minor detail is important when reassembling the barrel bridge as it means one doesn’t have to hold the barrel in place from the other side of the movement while re-attaching the ratchet wheel.

The barrel in the calibre 849 is a very nice piece of work. A hanging barrel is a questionable idea from an engineering standpoint but is something of a necessity if one wants to approach the kind of thinness that the calibre 849 achieves. JLC’s execution of the idea is quite respectable.

The problem with a hanging barrel (or a floating or standing barrel, the difference being which side it is supported on) is that the mainspring barrel, as the power supply to the entire mechanism, generates a significant amount of torque. When the central axis of the barrel is only supported on one side, the bearing surface is subjected to a considerable amount of additional lateral torque, and subsequently, wear.

To combat this problem, JLC has employed an ingeniously rugged two piece barrel arbor that pivots on a large diameter bearing surface both in the bridge and in the barrel drum itself. The larger bearing surface spreads the additional stress and wear over a larger area as well as allowing less side to side motion of the barrel. The two part barrel arbor is held together by three screws from inside the barrel [11], sandwiching the barrel drum between the two halves which are alone responsible for the endshake of the barrel.

One criticism I have of the barrel attachment is the lack of a jewel or bushing [12]. Even a well designed hanging arrangement as found in the calibre 849 is prone to stress the bearing surface more than a conventional barrel with two supported pivots. It would seem that a replaceable beryllium bronze bushing would be more appropriate (a jewel likely being too thin and fragile) than the unbushed bearing surface present.

The underside of the barrel bridge [12] has a milled recess for the click spring and, like the underside of all the bridges, is well finished. The milled portions to accommodate the wheels are perlaged and the mating surfaces have a uniform matte finish, exhibiting care and precision in their manufacture. The power train wheels have circular graining on top and the spokes and rim are chamfered on the topside as well. The undersides of the center and third wheel have a matte finish while, curiously, the fourth wheel is circular grained on both sides [13].

The Escapement, Balance and Hairspring

The escapement is well made and mostly unremarkable except for the oddly shaped and oddly finished pallet lever. One of many design decisions made to minimize the thickness of the movement, most of the pallet lever is on a lower plane than the fork horns. This arrangement keeps the pivots and jewels low enough to clear the low profile balance rim while raising the horns enough to clear the shock protection setting.

The pallet lever is more elaborate than those commonly seen even in high-grade watches of recent years but the chamfering that is present is very uneven near the step between the two levels of the pallet. It seems that the chamfer is applied by a machine or polishing disc of some kind that cannot get cleanly into the tight corners. The lever would be more attractive if no chamfer was present at all.

The incredibly delicate balance is the most obvious evidence of the ultrathin design. The arms of the balance have a clearly defined step [14] so that they can clear the hairspring stud. Although there is a steel safety roller, the impulse jewel is planted directly into the arms of the balance [15], thereby eliminating the need for an impulse roller and the fraction of a millimeter it would take up.

The balance is of a very large diameter for the size of the movement (8.4mm and 21.15mm in diameter respectively) and is polished on both sides with a series of small poising divots on the underside. Interestingly, there are also small divots around the outside of the rim [16], presumably made while the balance was in place either for dynamic poising or to center the regulator. The simple regulator is nicely made with curb pins and a separate boot [17] (the movable cover that keeps the hairspring from slipping out from between the pins).

The hairspring in the calibre 849 is anachronistic in almost every detail. Made of Nivarox 1, it is otherwise slightly archaic in terms of its shape and its methods of attachment. It is pinned at the stud and at the collet [18] and has a smooth terminal curve rather than a dogleg. While a smooth, well-formed terminal curve can function admirably, there is a certain amount of positional performance that can be gained with a properly formed dogleg. Similarly, there are some theoretical benefits to the more modern methods of hairspring attachment but there is a certain charm to the traditional handcraftsmanship exhibited by the pinned stud and collet.


The exterior of the Jaeger-LeCoultre Master Ultrathin is modern, both in its construction and the sleek lines of the case and hands. Inside, the movement is entirely traditional and exhibits a level of quality associated with timepieces from a bygone era. Its water resistance and solid, well-designed case make it completely appropriate for everyday use while its size and classic simplicity make it even better suited for a dress watch.

The Jaeger-LeCoultre Master Ultrathin represents a remarkable bargain in the modern mechanical watch market. It is classic yet modern looking and incredibly robust for an ultrathin watch while exhibiting the quality of old-world craft that cannot otherwise be had for several times its asking price. The elegant design of the ultrathin movement and the fine finishing touches give it a singular position in the current market. It provides the lion’s share of what is expected from first tier mechanical watches at a surprisingly affordable price. The security of knowing the watch was tested for 1000 hours by Jaeger-LeCoultre only adds to its attractiveness. Many watch companies could learn something about high integrity watchmaking from Jaeger-LeCoultre. They are a bright light in the sometimes cynical world of the high-mech renaissance.



At a time when watches are getting bigger and bigger, it is easy to forget a watch like the Jaeger-LeCoultre Master Ultra Thin.

Fashion comes and goes, but the JLC Master Ultra Thin is still the same classic-looking watch that impresses. This understated model has not aged after all these years and is still on the wrists of many watch lovers today.

Despite the obvious lack of heft, this watch is surprisingly comfortable on the wrist and at times, you may even forget that it is being worn!

The lack of seconds-hand is impractical but more fitting to its clean look. The leather strap is a little tough when new but not to the extent of being uncomfortable. The strap should be more flexible after a few days of use.

Partly because of the current big watch trend, this model is one of those rare elegant watches that can be worn by owners of both genders.


I have owned the Master Ultra Thin in Rose Gold/Silver White Dial for several years. I purchased it during my early years of serious watch collecting. It represented the perfect combination of excellent craftsmanship using a brilliant in-house movement, uniqueness in its thinness, affordability, and beautiful appearance. Clearly, it's the most elegant watch I own with its simple, clean dial with simple markers and half frosted dauphine hands. It is so light and thin you hardly are aware of its presence. This model is fitted with a high gloss crocodile strap and gold deployment buckle.

Although 34mm in diameter it appears slightly larger on my 7" wrist, probably because of the relatively large dial and small case surround. It is purely minimalist in size and in appearance. No minute markers, no luminosity, no second hand, no date, no applied logo - simple black printing. The case is beautifully designed to make the thin watch look even thinner, with the outer circumference approaching a knife edge. The lugs are delicately shaped, becoming thicker at the ends to accept the spring pins. In fact the case is so thin it makes the standard size leather band and deployment clasp appear thick. Another nice touch is the leather band is curved to hug the case. The JLC Master Ultra Thin is a good representative of the value JLC watches provide. A finely made in-house movement, excellent casework and dial, all for a reasonable price.

In spite of all elements working so well, for some reason I wear this watch only for dressy occasions. Clearly it is a formal dress watch with the black strap. The watch has performed flawlessly over the years and has been quite accurate. It is a pleasure to wind and holds over a 40 hr reserve. The back on this model is solid gold engraved with the Master Control seal, the model and serial numbers.


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Copyright February 2003 - John Davis and - all rights reserved