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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →The Longines HydroConquest GMT and Seiko Prospex SPB381 are automatic GMT dive watches with roughly 72 hours of stated power reserve. The main differences are practical: the representative 41 mm Longines is rated to 300 m and highlights a silicon balance spring, while Seiko’s 42 mm SPB381 is rated to 200 m and explicitly documents independent one-hour adjustment of its GMT hand. Choose based on how you set a second time zone, how each watch fits, your water-use needs, and like-for-like pricing—not on an assumption that either is universally better.
At a glance: the main differences
This comparison uses the Longines HydroConquest GMT reference L3.790.4.56.6, a 41 mm steel-bracelet version, and the Seiko Prospex SPB381, the green-dial version of Seiko’s 2023 reinterpretation of its 1968 diver design. HydroConquest GMT models vary by configuration, so confirm the exact reference, dial, and strap or bracelet before buying.
| # | Preview | Product | Price | |
|---|---|---|---|---|
| 1 |
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HYDROCONQUEST 41MM Automatic Watch | $3,350.00 | Buy on Amazon |
| 2 |
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HYDROCONQUEST 41MM Automatic Watch | $1,600.00 | Buy on Amazon |
| 3 |
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HYDROCONQUEST 41MM Automatic Watch | $2,000.00 | Buy on Amazon |
| 4 |
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HYDROCONQUEST 41MM Automatic Watch | $3,350.00 | Buy on Amazon |
| 5 |
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HYDROCONQUEST 41MM Automatic Watch | $1,600.00 | Buy on Amazon |
| Specification | Longines HydroConquest GMT L3.790.4.56.6 | Seiko Prospex SPB381 |
|---|---|---|
| Case diameter | 41 mm | 42.0 mm |
| Other case dimensions | Not listed in the reviewed product specifications (Longines) | 12.9 mm thick; 48.6 mm lug-to-lug; 20 mm lug width (Seiko) |
| Water resistance | 30 bar / 300 m | 200 m / 660 ft, diver’s |
| Power reserve | Up to 72 hours | Approximately 72 hours / three days |
| Movement | Self-winding mechanical; 25,200 vibrations per hour; silicon balance spring and magnetic-field resistance stated by Longines | Caliber 6R54; automatic with manual winding; 24 jewels; stated precision +25/-15 seconds per day |
| GMT operation | GMT function listed; adjustment method not explained on the reviewed product page | GMT hand adjusts independently in one-hour increments without interrupting the time-of-day hands |
| Bezel and crown | Stainless-steel and ceramic bezel; unidirectional; screw-in crown | Stainless-steel bezel with ceramic display; unidirectional; screw-down crown |
| Crystal and lume | Scratch-resistant sapphire with anti-reflective coating on both sides; Super-LumiNova | Sapphire with inner-surface anti-reflective coating; LumiBrite on hands, indices, and bezel |
| Bracelet and clasp | Steel bracelet; double-security folding clasp with micro-adjustment | Three-link steel bracelet; clasp with secure lock and extender listed in regional specifications |
| Manufacturer price captured | US$3,350 for the steel-bracelet reference; a 41 mm rubber-strap variant was listed at US$3,150 | A directly comparable current US price was not established from the cited official Seiko page |
Specifications and the captured Longines US prices come from the Longines US product page. Seiko dimensions and movement specifications are from its SPB381 specification page; GMT operation and collection history are described on the Seiko 1968 GMT collection page. These are manufacturer specifications, not results of side-by-side testing.
How the GMT functions differ
Seiko: a documented independent hour adjustment
Seiko says the SPB381’s GMT hand can be set independently in one-hour increments without interrupting the time-of-day hands. That is useful when travelling across time zones: the local hour can be changed while the main time display continues running. The independently adjustable hand can also track another zone, though the one-hour steps matter if you regularly use a time zone offset by a half-hour or quarter-hour.
#1 Best Overall
- Automatic L844 movement, hours, minutes, seconds and date. 24 hours hand with time zone mechanism Screw-down case back
- Stainless steel with double security folding clasp with micro adjustment system
- 5 Year International Warranty
Longines: confirm the setting procedure for your reference
The cited Longines page identifies a GMT function but does not explain how its hands adjust. Do not assume its setting behavior matches the Seiko’s. Before purchase, check the official manual for the exact HydroConquest GMT reference and confirm which hand moves when setting local time.
Fit: compare more than case diameter
The SPB381 is 42 mm across, compared with 41 mm for the cited Longines. A one-millimetre difference alone cannot determine which will sit better on a particular wrist. Seiko publishes a 48.6 mm lug-to-lug length and 12.9 mm thickness for the SPB381; the reviewed Longines specification page did not list equivalent dimensions. Try both on if possible, and pay attention to how the case ends meet your wrist as well as the watch’s thickness and bracelet fit.
Rank #2
- Automatic L888 movement, hours, minutes, seconds and date Screw-down case back
- Stainless steel with double safety folding clasp
- 5 Year International Warranty
Water resistance and movement specifications
What the depth ratings tell you
Longines rates the cited reference to 30 bar / 300 m; Seiko rates the SPB381 to 200 m / 660 ft as a diver’s watch. Those are the manufacturers’ published ratings. The higher Longines figure is a specification difference, not evidence here of superior real-world durability or a reason by itself to choose one for everyday wear.
Power reserve, magnetic resistance, and stated precision
Both brands state about three days of power reserve. Longines highlights a silicon balance spring and resistance to magnetic fields, while Seiko publishes a +25/-15 seconds-per-day precision specification for its 6R54 movement. These figures describe manufacturer claims; no independent comparative accuracy, water-resistance, or power-reserve testing is available here.
Rank #3
- Automatic L888 movement, hours, minutes, seconds, and date. Screw-down case back
- Stainless steel with double safety folding clasp
Bracelet and clasp details
The cited Longines steel-bracelet reference has a double-security folding clasp with micro-adjustment. Seiko lists a secure-lock clasp and extender for the SPB381 in regional specifications. The descriptions do not establish that either bracelet offers tool-free, on-the-fly adjustment. If clasp adjustment is important, inspect the exact bracelet and ask how its adjustment works before purchase.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Price and model availability
The Longines US page captured for this comparison listed the steel-bracelet L3.790.4.56.6 at US$3,350 and a 41 mm rubber-strap version at US$3,150. These are configuration-specific US manufacturer prices captured in 2026 and may change. The cited Seiko specification page is for the Malaysian market, and a directly comparable current US price was not established. Check current prices for the exact references in the same market, with matching condition, taxes, and warranty, before making a value comparison.
Quick Recap
Best Value
- Automatic L888 movement, hours, minutes, seconds and date Screw-down case back
- Stainless steel with double safety folding clasp
- 5 Year International Warranty
Rank #4
- Automatic L844 movement, hours, minutes, seconds and date. 24 hours hand with time zone mechanism Screw-down case back
- Stainless steel with double security folding clasp with micro adjustment system
- 5 Year International Warranty
Which one should you choose?
- Choose the Seiko SPB381 if independently adjusting the GMT hand in one-hour increments is central to how you travel or track another time zone, and its measured dimensions work for your wrist.
- Consider the Longines if its 300 m rating, silicon balance spring specification, bracelet configuration, or design better matches your priorities. Verify the GMT setting procedure for the exact reference before relying on a particular travel workflow.
- Try both before deciding if fit or clasp comfort is decisive; published diameters and clasp descriptions cannot establish how either watch will wear on your wrist.
- Compare current, equivalent offers using the same country, reference configuration, new or used condition, taxes, and warranty. The captured prices do not support a direct US price comparison between these two models.
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.
