PC Slower Than It Used to Be?
A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Crashes, No Sound, or Screen Glitches?
Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteThe current steel Jaeger-LeCoultre Master Ultra Thin Power Reserve is reference Q1378421: a 39 mm automatic dress watch with a specified 70-hour reserve. It is materially different from the older Q1378420, which Jaeger-LeCoultre lists as out of collection and specifies with a 43-hour reserve and a thicker case. If you are considering one, check the reference first; the name alone does not identify which generation or specifications you are buying.
Which watch is this review about?
Jaeger-LeCoultre’s current Swiss English product page identifies the stainless-steel Master Ultra Thin Power Reserve as Q1378421. The collection name is also commonly rendered as “Réserve de Marche.” This review uses the current Q1378421 as its main subject and treats Q1378420 as the older generation, not as an interchangeable version.
The maker marks Q1378420 “Out of collection.” It is a useful reference when evaluating pre-owned listings, but its specifications should not be carried over to Q1378421. The earlier watch was reported at its 2012 launch as a 39 mm model with a 43-hour reserve.
Q1378421 specifications
| Specification | Current Q1378421 |
|---|---|
| Case | Stainless steel; 39 mm diameter and 8.95 mm thick, per Jaeger-LeCoultre |
| Water resistance | 5 bar, per Jaeger-LeCoultre |
| Movement | Automatic Calibre 938 with a silicon escapement, per Jaeger-LeCoultre |
| Power reserve | 70 hours, per Jaeger-LeCoultre |
| Movement details | 28,800 vibrations per hour (4 Hz), 262 components, 39 jewels and one barrel, per Jaeger-LeCoultre |
| Functions | Hours and minutes, seconds, date and power-reserve indication |
| Strap | Black alligator strap; 21 mm lug width and quick-release technology, per Jaeger-LeCoultre |
These are manufacturer specifications, not independent test results. The maker describes the caseback as showing the movement.
#1 Best Overall
- Strap Material: Crafted from premium full-grain leather, the surface features a specially treated worn effect for a vintage look. The inner side in contact with the wrist is lined with comfortable artificial suede. Paired with classic color-block stitching and a sturdy stainless steel buckle, these straps strike the perfect balance between durability and style. Suitable for various occasions, they are ideal for both casual and formal wear.
- Size Selection: Before purchasing, please confirm the strap size compatible with your watch. The distance between the lugs where the strap connects to the watch case determines the strap width. The strap will only fit your watch if its width matches the lug width of your watch.
- Strap Adjustment: Featuring multiple adjustment holes for a worry-free fit. With more than 12 adjustment holes, it ensures precise fitting for various wrist sizes.
- Package Contents: Your order will include 1 genuine leather strap, one pair of spring bars, and a spring bar tool.
- Worry-Free After-Sales Service: We offer a "90-Day No-Hassle Replacement" service. Is the strap fading? Does it not meet your expectations in terms of texture? As long as there is no human-induced damage, we will replace it for you directly! For custom requests, please feel free to contact our customer service. Thank you for your purchase!
What does the power reserve mean in use?
A 70-hour reserve is the manufacturer’s stated running time after the watch is fully wound, assuming it is not rewound while running. Jaeger-LeCoultre says “there is no need to wind the watch, even after a whole weekend without wearing it.” That is the manufacturer’s description of the reserve, not a separately measured result.
The Q1378421 has a power-reserve indicator, so the dial provides an indication of remaining running time. The movement specification lists one barrel. The older Q1378420 is specified at 43 hours, a difference of 27 hours from the current model’s stated reserve.
Rank #2
- Strap Material: Crafted from premium full-grain leather, the surface features a specially treated worn effect for a vintage look. The inner side in contact with the wrist is lined with comfortable artificial suede. Paired with classic color-block stitching and a sturdy stainless steel buckle, these straps strike the perfect balance between durability and style. Suitable for various occasions, they are ideal for both casual and formal wear.
- Size Selection: Before purchasing, please confirm the strap size compatible with your watch. The distance between the lugs where the strap connects to the watch case determines the strap width. The strap will only fit your watch if its width matches the lug width of your watch.
- Strap Adjustment: Featuring multiple adjustment holes for a worry-free fit. With more than 12 adjustment holes, it ensures precise fitting for various wrist sizes.
- Package Contents: Your order will include 1 genuine leather strap, one pair of spring bars, and a spring bar tool.
- Worry-Free After-Sales Service: We offer a "90-Day No-Hassle Replacement" service. Is the strap fading? Does it not meet your expectations in terms of texture? As long as there is no human-induced damage, we will replace it for you directly! For custom requests, please feel free to contact our customer service. Thank you for your purchase!
How Q1378421 differs from Q1378420
| Q1378421 (current) | Q1378420 (older) | |
|---|---|---|
| Collection status | Listed on Jaeger-LeCoultre’s current product page | Marked “Out of collection” on Jaeger-LeCoultre’s page |
| Case diameter | 39 mm | 39 mm |
| Case thickness | 8.95 mm | 9.9 mm |
| Power reserve | 70 hours | 43 hours |
| Movement details | Automatic Calibre 938 with a silicon escapement; 28,800 vibrations per hour, 262 components, 39 jewels and one barrel, per the current specification | The cited Jaeger-LeCoultre page lists the reserve and case dimensions; comparable movement details are not stated there |
The dimensions and reserve above come from the respective Jaeger-LeCoultre product pages. A 2012 report on the original model also gives the older 43-hour reserve. Because Q1378420 is out of collection, a pre-owned example’s condition and service history matter alongside its generation-specific specifications.
What is the dial and case design?
Jaeger-LeCoultre describes Q1378421’s dial as silvered grey with sunray brushing, elongated hour markers, double-finished Dauphine hands, an applied logo, opaline counters and a minute track. The functions are arranged around hours and minutes, seconds, a date display and the power-reserve indication. Curved lugs are part of the manufacturer’s case description.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Rank #3
- Selected calf leather, leather shoes feel soft and comfortable, and the body of the watch as one!
- The bottom leather is comfortable, soft, breathable, waterproof and sweatproof, which can effectively resist the erosion of sweat and prevent odour.
- The clasp is made of 316 stainless steel, polished meticulously and stable without fading.
- Please measure the lug width before ordering, the lug width must be exactly the same as the selected strap width to ensure accurate wearing.
- A set of matching spring bars and installation tools are included.
Those details establish the design and features, but not how legible the indications are in different lighting, how the watch feels on a particular wrist, or whether its finishing meets an individual buyer’s expectations. Those judgments require seeing and wearing the specific watch.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is it worth buying?
Q1378421 is the clearer choice if your priority is the current specification: it is thinner on paper than Q1378420 and has a substantially longer stated reserve. Whether it is worth buying depends on the example, its price and your preference for the dial and complications; current pricing and live inventory are not established here.
Rank #4
- Strap Material: Crafted from premium full-grain leather, the surface features a specially treated worn effect for a vintage look. The inner side in contact with the wrist is lined with comfortable artificial suede. Paired with classic color-block stitching and a sturdy stainless steel buckle, these straps strike the perfect balance between durability and style. Suitable for various occasions, they are ideal for both casual and formal wear.
- Size Selection: Before purchasing, please confirm the strap size compatible with your watch. The distance between the lugs where the strap connects to the watch case determines the strap width. The strap will only fit your watch if its width matches the lug width of your watch.
- Strap Adjustment: Featuring multiple adjustment holes for a worry-free fit. With more than 12 adjustment holes, it ensures precise fitting for various wrist sizes.
- Package Contents: Your order will include 1 genuine leather strap, one pair of spring bars, and a spring bar tool.
- Worry-Free After-Sales Service: We offer a "90-Day No-Hassle Replacement" service. Is the strap fading? Does it not meet your expectations in terms of texture? As long as there is no human-induced damage, we will replace it for you directly! For custom requests, please feel free to contact our customer service. Thank you for your purchase!
Before buying, especially pre-owned, use this checklist:
Quick Recap
Best Value
- Strap Material: Crafted from premium full-grain leather, the surface features a specially treated worn effect for a vintage look. The inner side in contact with the wrist is lined with comfortable artificial suede. Paired with classic color-block stitching and a sturdy stainless steel buckle, these straps strike the perfect balance between durability and style. Suitable for various occasions, they are ideal for both casual and formal wear.
- Size Selection: Before purchasing, please confirm the strap size compatible with your watch. The distance between the lugs where the strap connects to the watch case determines the strap width. The strap will only fit your watch if its width matches the lug width of your watch.
- Strap Adjustment: Featuring multiple adjustment holes for a worry-free fit. With more than 12 adjustment holes, it ensures precise fitting for various wrist sizes.
- Package Contents: Your order will include 1 genuine leather strap, one pair of spring bars, and a spring bar tool.
- Worry-Free After-Sales Service: We offer a "90-Day No-Hassle Replacement" service. Is the strap fading? Does it not meet your expectations in terms of texture? As long as there is no human-induced damage, we will replace it for you directly! For custom requests, please feel free to contact our customer service. Thank you for your purchase!
- Verify the reference. Match the listing and watch documentation to Q1378421 or Q1378420 rather than relying only on the collection name or photographs.
- Compare specifications to the reference. A 70-hour reserve and 8.95 mm case correspond to the current Q1378421; the older Q1378420 is listed at 43 hours and 9.9 mm thick.
- Review condition and service records. Ask for documentation and have the watch’s condition assessed; the published specifications do not establish the state of an individual example.
- Check the seller. Confirm the seller’s identity and authorization directly, and verify current availability and terms before purchase. No seller authorization or live stock is established by the product specifications.
- Confirm strap fit before ordering alternatives. Jaeger-LeCoultre lists a 21 mm quick-release strap for Q1378421. Width alone does not prove a third-party strap will fit its attachment system.
Sources
- Jaeger-LeCoultre: Q1378421 product specifications
- Jaeger-LeCoultre: Q1378421 description and reserve statement
- Jaeger-LeCoultre: Q1378420 specifications and collection status
- Time and Watches: February 2012 report on the original model
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
