The Seiko NH70 represents a departure from the workhorse NH35 that dominates affordable mechanical watches. Where the NH35 prioritizes reliability and cost-effectiveness, the NH70 emphasizes visual appeal and refined performance. This open-heart movement beats at 28,800 vibrations per hour—a full 33% faster than its NH35 sibling—while measuring thinner despite exposing the balance wheel through a dial cutout. It's Seiko's answer to customers who want something more visually engaging than a standard three-hand automatic.
Understanding the NH70 helps you evaluate watches using this movement and decide whether its premium features justify the higher cost compared to the NH35. This guide explains what makes the NH70 unique, how it compares to other Seiko calibers, and whether it's worth the investment for your next watch purchase or modding project.
What is the Seiko NH70 Movement?
The NH70 is a high-beat automatic movement from Seiko's NH family, designed specifically for open-heart dial configurations. Unlike standard movements hidden entirely beneath the dial, the NH70 positions its balance wheel to be visible through a cutout, creating the "open-heart" or "open aperture" effect that showcases the beating heart of the mechanism.
Introduced as part of Seiko's effort to offer more premium NH-series calibers, the NH70 operates at 28,800 vibrations per hour (4 Hz)—the same frequency as many Swiss movements and significantly higher than the 21,600 vph of the NH35. This higher beat rate produces smoother sweeping seconds and potentially better accuracy, though the official specifications remain the same as other NH movements.
The movement is commonly found in Seiko's Presage Cocktail Time watches and other dress-oriented models where the open-heart design adds visual interest to otherwise simple dials. It's positioned as a step up from the NH35/NH36, commanding a price premium that reflects its specialized design and higher beat rate.
Technical Specifications
Understanding the NH70's specifications reveals how it differs from other Seiko calibers and what performance you can expect.
Core Specifications
- Beat rate: 28,800 vibrations per hour (4 Hz, 8 beats per second)
- Jewels: 24
- Power reserve: 41 hours
- Accuracy: -20 to +40 seconds per day (factory specification)
- Thickness: 4.98mm
- Diameter: 27.4mm
- Winding: Automatic with manual winding capability
- Hacking: Yes (seconds hand stops when crown is pulled)
- Direction: Bidirectional automatic winding
- Complications: None (time-only on NH70; date on NH72)
What the Specifications Mean
28,800 vph beat rate: The balance wheel oscillates 28,800 times per hour, or eight times per second. This creates a smoother sweeping motion for the seconds hand compared to the six-beats-per-second of 21,600 vph movements. The higher frequency also divides time into smaller increments, potentially improving accuracy.
4.98mm thickness: Despite the higher beat rate, the NH70 measures thinner than the 5.32mm NH35. This enables slimmer watch cases—critical for dress watches where every millimeter matters. The reduced thickness comes from engineering refinements rather than removing components.
41-hour power reserve: Identical to the NH35 despite the higher beat rate. Higher frequencies typically consume more energy, so maintaining the same power reserve as the slower NH35 is noteworthy. You can take the watch off Friday evening and it will still be running Sunday morning.
24 jewels: These synthetic ruby bearings reduce friction at critical pivots, extending service intervals and improving accuracy. The jewel count matches the NH35, indicating similar overall construction quality.
How the NH70 Works
The NH70 operates using the same fundamental principles as all automatic movements but incorporates design elements specifically for the open-heart configuration.
Open-Heart Design
The defining feature of the NH70 is its open-heart layout. The balance wheel—the oscillating component that regulates timekeeping—is positioned to align with a cutout in the dial, typically between 6 and 8 o'clock. This exposes the balance wheel, hairspring, and pallet fork, allowing wearers to see the movement in action.
Unlike skeleton watches that expose the entire movement, open-heart designs reveal only the escapement area. This provides mechanical interest while maintaining a traditional dial layout for the rest of the watch face. The balance wheel's oscillations are hypnotic—eight visible beats per second create fluid motion.
Automatic Winding Mechanism
Like other NH-series movements, the NH70 uses a weighted rotor that spins with wrist motion. This rotor connects to a bidirectional winding mechanism—it winds the mainspring regardless of which direction it rotates. As you move throughout the day, the rotor's inertia keeps the mainspring tensioned, maintaining the 41-hour power reserve.
The movement also includes manual winding capability accessed through the crown. If the watch has stopped after sitting unworn for two days, you can wind it manually rather than shaking it to engage the automatic winding. This hybrid approach offers flexibility: rely on automatic winding during wear or manually wind for instant full power reserve.
Escapement and Regulation
The escapement controls energy release from the mainspring to the gear train. The balance wheel oscillates at its natural frequency (28,800 times per hour), with each oscillation allowing the escape wheel to advance one tooth. The pallet fork locks and unlocks the escape wheel in synchronization with the balance wheel's oscillations.
This precise interaction between components determines the movement's accuracy. The NH70 includes a regulator for fine-tuning the effective length of the hairspring, allowing watchmakers to adjust daily rate within a few seconds per day.
NH70 vs NH35: Key Differences
The NH35 and NH70 share the NH-series DNA but diverge in significant ways that affect performance, appearance, and cost.
Beat Rate Comparison
NH70: 28,800 vph (8 beats per second)
NH35: 21,600 vph (6 beats per second)
The NH70's higher beat rate produces noticeably smoother sweeping seconds. While both create the characteristic mechanical "sweep," the NH70's eight beats per second flows more fluidly. This difference is particularly apparent when viewed at close range or in slow motion.
Higher beat rates also theoretically improve accuracy by dividing time into smaller increments, though official specifications don't reflect this—both movements claim -20/+40 seconds per day. In practice, individual NH70 examples may regulate more precisely than individual NH35 examples, but this varies by unit.
Thickness Comparison
NH70: 4.98mm
NH35: 5.32mm
The NH70 is 0.34mm thinner—about 6% reduction. This enables slimmer case designs, particularly important for dress watches worn under shirt cuffs. A watch using NH70 might achieve a 10mm total thickness where an NH35 version would measure 10.5mm. That half-millimeter difference affects how the watch wears and whether it slides comfortably under clothing.
Visual Design
NH70: Designed for open-heart dials with balance wheel cutout
NH35: Standard configuration with fully covered dial
The NH70 requires dials with open-heart cutouts to showcase the balance wheel. You can't use a standard closed dial with an NH70 without wasting its primary design feature. Conversely, the NH35 works with any dial design—open-heart, traditional, minimalist, or complex.
Price Comparison
NH70: $80-$120 from parts suppliers
NH35: $30-$50 from parts suppliers
The NH70 costs 2-3 times more than the NH35. This reflects the higher beat rate, slimmer profile, and more specialized application. For watch modders, this price difference significantly impacts build budgets. For buyers, watches using NH70 typically cost $100-$200 more than comparable NH35 models.
Parts Ecosystem
NH70: Limited—dozens of compatible dials and hands
NH35: Extensive—thousands of compatible parts
The NH35 dominates the modding world, resulting in enormous parts selection. The NH70's specialized open-heart requirement limits compatible dials to those specifically designed with balance wheel cutouts. This restricts customization options and makes sourcing replacement parts more challenging.
Use Cases
NH70: Dress watches, open-heart designs, visual appeal priority
NH35: Dive watches, field watches, tool watches, budget builds
The NH70 suits watches where aesthetics and refinement matter more than cost. Dress watches, cocktail-time pieces, and designs emphasizing mechanical beauty benefit from the NH70's open-heart showcase and slim profile. The NH35 suits practical applications—dive watches, daily wearers, and builds where movement visibility doesn't matter.
NH70 vs NH72: Understanding the Difference
Seiko offers the NH70 movement in two variants that differ only in date complication.
NH70 (No Date)
- Time-only display
- Clean dial without date window
- Symmetrical design options
- Requires no date wheel
NH72 (With Date)
- Date display at 3 o'clock
- Same specifications as NH70 otherwise
- Requires dial with date window
- Slightly higher cost ($85-$130)
Which to Choose?
Choose the NH70 if you prefer clean, symmetrical dials without date complications. The absence of a date window creates minimalist elegance particularly suited to dress watches. Choose the NH72 if you actually use the date function in daily wear. The practical utility of knowing the date may outweigh aesthetic purity.
Both movements are mechanically identical in timekeeping performance, power reserve, and reliability. The choice comes down to whether you want a date display and whether you can find a dial you like with or without a date window.
Advantages of the NH70 Movement
Smoother Sweeping Seconds
The 28,800 vph beat rate creates eight visible ticks per second, producing notably smoother motion than the NH35's six beats per second. For watch enthusiasts who appreciate the mechanical sweep, this difference is immediately noticeable and aesthetically pleasing.
Thinner Profile
At 4.98mm, the NH70 enables dress watch cases under 10mm total thickness. This matters for formal wear where the watch should slide easily under a shirt cuff. The 0.34mm advantage over the NH35 may seem small, but it's the difference between a sleek dress watch and one that feels bulky.
Open-Heart Visual Appeal
Watching the balance wheel oscillate provides constant mechanical interest. Unlike static dials, the open-heart design showcases the beating heart of the watch—a mesmerizing reminder that you're wearing a mechanical device, not an electronic one. This appeals to enthusiasts who appreciate visible mechanics.
Better Accuracy Potential
While factory specifications match the NH35, the higher beat rate provides finer time division. A well-regulated NH70 may achieve better real-world accuracy than a typical NH35. Some owners report daily rates within ±3-5 seconds after regulation, though individual variation exists.
Premium Positioning
The NH70 represents a step up from the ubiquitous NH35. Watches using NH70 signal slightly higher quality and attention to detail, differentiating them from the mass of NH35-powered pieces. For buyers seeking something beyond the entry level, the NH70 delivers tangible upgrades.
Disadvantages of the NH70 Movement
Higher Cost
At $80-$120 for the movement alone, the NH70 costs 2-3 times more than the NH35. For watch modders, this significantly impacts build budgets. For buyers, NH70 watches typically cost $100-$200 more than equivalent NH35 models. This premium may not be justified if you don't specifically value the open-heart design or higher beat rate.
Limited Parts Ecosystem
The NH70's specialized design means fewer compatible dials, hands, and cases. While the NH35 has thousands of aftermarket dials available, the NH70 has dozens. This limits customization options and makes replacement parts harder to source if needed.
Open-Heart Design Requirement
The NH70 is designed around the balance wheel cutout. Using it without an open-heart dial wastes its primary feature. If you want a traditional closed dial, the NH35 makes more sense both functionally and economically. The NH70 locks you into a specific aesthetic.
Less Common in Modding
Fewer modders use NH70 movements due to higher cost and limited parts. This means less community support, fewer build guides, and more troubleshooting on your own. The NH35's ubiquity provides extensive documentation and community knowledge.
Same Official Accuracy
Despite the higher beat rate, Seiko rates both NH70 and NH35 at -20/+40 seconds per day. While the NH70 may regulate more precisely in practice, you're paying a premium for a feature that isn't officially guaranteed to improve performance.
Watches Using the NH70 Movement
The NH70 appears primarily in Seiko's own watches and a limited selection of microbrands that prioritize visual appeal.
Seiko Presage Cocktail Time Series
The Presage Cocktail Time watches (SSA, SRPB series) extensively use the NH70 and NH72 movements. These dress watches feature elegant dials with open-heart cutouts at 6 o'clock, showcasing the balance wheel through cocktail-themed colors and textures. Models like the SSA343 (Mockingbird) and SRPB41 (Blue Moon) have become iconic examples of affordable open-heart watches.
Price range: $300-$500 depending on model and retailer
Seiko Presage SSA Series
The SSA line includes various open-heart models using NH70/NH72 movements. These watches range from traditional dress designs to more contemporary interpretations, all featuring the signature balance wheel cutout.
Microbrands and Independent Makers
Some microbrands use NH70 movements in dress watch offerings where the open-heart design adds uniqueness. However, the higher movement cost and limited parts selection mean fewer microbrands adopt it compared to the NH35.
Custom and Modded Watches
A small segment of the modding community uses NH70 movements for custom dress watch builds. These typically target buyers specifically seeking open-heart designs and willing to pay the premium for higher beat rate and slim profile.
NH70 in Watch Modding
The NH70 occupies a niche position in the modding world—appreciated by some, avoided by others.
When NH70 Makes Sense for Modding
- Dress watch builds: The slim profile and refined beat rate suit formal timepieces
- Open-heart designs: If showcasing the movement is your goal, the NH70 is purpose-built
- Premium builds: When you want to differentiate from standard NH35 watches
- Personal watches: Building for yourself rather than resale justifies the premium
Why Modders Often Choose NH35 Instead
- Cost: The $50-$90 price difference buys a sapphire crystal or ceramic bezel insert
- Versatility: NH35 works with any dial design, not just open-heart
- Parts availability: Thousands of compatible dials vs dozens for NH70
- Proven track record: More modders use NH35, providing better support
NH70 Modding Considerations
If you choose to mod with an NH70, plan carefully:
- Source the dial first—ensure open-heart cutout aligns with the balance wheel position
- Verify hand compatibility—NH70 uses the same hand sizes as NH35 but confirm fitment
- Check case compatibility for the 4.98mm movement height
- Budget appropriately for the higher movement cost
- Accept limited future dial options if you want to change the look later
Some modders and small brands incorporate NH70 movements into dress watch designs where the slimmer profile and open-heart aesthetic justify the additional cost. However, this represents a small fraction of the modding market compared to NH35 dominance.
Servicing and Maintenance
Service Intervals
Like all mechanical movements, the NH70 benefits from periodic maintenance. Recommended service intervals:
- Daily wear: Service every 5-7 years
- Occasional wear: Service every 7-10 years
- After water exposure: Service immediately if water enters the case
Service involves disassembly, cleaning, lubrication, adjustment, and reassembly. This maintains accuracy and extends the movement's lifespan.
Parts Availability
NH70 parts are available through Seiko service centers and some parts suppliers, though selection is more limited than NH35. Common service parts (mainspring, balance complete, pallet fork) are obtainable, but exotic components may require longer lead times.
Service Costs
Expect to pay $75-$150 for a complete NH70 service depending on location and provider. This is comparable to NH35 service costs—watchmakers charge similar rates regardless of the specific NH-series caliber.
Alternatively, the movement can be replaced entirely for $80-$120 if damage is extensive or service costs approach replacement cost. This is common practice with affordable movements where service costs approach or exceed replacement cost.
Regulation Potential
The NH70 can be regulated for improved accuracy. A skilled watchmaker using a timegrapher can adjust daily rate to ±5 seconds or better in most positions. The higher beat rate may allow finer regulation than the NH35, though this depends on individual movement quality.
Regulation typically costs $30-$50 as a standalone service or is included in complete servicing.
Is the NH70 Worth the Premium?
Whether the NH70 justifies its higher cost depends on your priorities and use case.
The NH70 Makes Sense If:
- You want open-heart design: The NH70 is purpose-built for this aesthetic
- Smooth sweep matters to you: The 28,800 vph beat rate is noticeably smoother
- You're building a dress watch: The 0.34mm thickness advantage helps achieve slim profiles
- You appreciate higher beat rates: The refined tick appeals to movement enthusiasts
- Budget allows the premium: The extra $50-$90 doesn't strain your overall budget
The NH35 Makes More Sense If:
- You want maximum value: The NH35 delivers 80% of the performance at 40% of the cost
- Open-heart doesn't appeal: Without using the cutout feature, the premium is wasted
- You want dial variety: The NH35's massive parts ecosystem provides endless options
- Building on a budget: The $50-$90 savings buy meaningful upgrades elsewhere
- You prefer tool watches: Dive watches and field watches don't benefit from NH70 features
Real-World Value Assessment
For most buyers and modders, the NH35 provides better overall value. Its lower cost, broader compatibility, and proven track record make it the default choice. The NH70 serves a specific niche—dress watches and open-heart designs where its unique features justify the premium.
If you're drawn to a specific watch using an NH70 (like a Presage Cocktail Time), the movement choice is already made for you. Evaluate the complete package rather than the movement in isolation. A $400 Presage with NH70 may deliver more satisfaction than a $300 watch with NH35 if the overall design resonates with you.
Frequently Asked Questions
NH70 vs NH35: Which is better?
Neither is objectively "better"—they serve different purposes. The NH70 offers higher beat rate (28,800 vph), slimmer profile (4.98mm), and open-heart design at 2-3x the cost. The NH35 provides proven reliability, massive parts ecosystem, and lower cost. Choose NH70 for dress watches and open-heart designs; choose NH35 for everything else.
Is the NH70 more accurate than the NH35?
Official specifications are identical (-20/+40 seconds per day), but the NH70's higher beat rate may allow more precise regulation in practice. Some owners report better accuracy with NH70, but individual variation between units matters more than the caliber difference. Both can be regulated to ±5 seconds per day.
Can you close the open-heart on an NH70?
Technically yes—you could use a standard dial without a cutout. However, this wastes the NH70's primary design feature and makes the premium cost unjustifiable. If you want a closed dial, use an NH35 and save $50-$90.
Where to buy NH70 movements?
NH70 movements are available from watch parts suppliers including Namoki Mods, Crystal Times, and eBay sellers specializing in Seiko movements. Expect to pay $80-$120 for genuine movements. Verify authenticity—some sellers may list NH70 when actually selling NH35.
What watches use the NH70?
The NH70 appears primarily in Seiko Presage Cocktail Time models (SSA and SRPB series). Some microbrands and custom modders also use it for dress watch builds. It's far less common than the NH35, appearing mainly in watches where the open-heart design is intentional.
Can the NH70 be regulated?
Yes. The NH70 includes a regulator allowing watchmakers to adjust daily rate. With proper regulation using a timegrapher, most NH70 movements can achieve ±5 seconds per day or better. The higher beat rate may enable finer regulation than the NH35.
Is the NH70 reliable?
Yes. The NH70 shares the same fundamental architecture as other NH-series movements, which have proven extremely reliable across millions of watches. Expect the same longevity as an NH35—decades of service with proper maintenance.
Why is the NH70 thinner than the NH35 despite higher beat rate?
The NH70's slimmer profile (4.98mm vs 5.32mm) results from engineering refinements in component layout and case design, not from removing features. Seiko optimized the movement architecture to achieve the reduced thickness specifically for dress watch applications.
Conclusion
The Seiko NH70 occupies a specialized position in the NH-series family. It's not a replacement for the NH35 but rather a complementary offering for specific applications—dress watches, open-heart designs, and builds where slim profile and refined beat rate justify the premium cost.
For buyers considering NH70-powered watches like the Seiko Presage Cocktail Time series, the movement delivers genuine value through its open-heart showcase, smooth 28,800 vph sweep, and dress-appropriate slim profile. These watches offer accessible entry to higher-beat movements and visible mechanical appeal that standard dial watches can't match.
For modders and DIY builders, the NH70 presents challenges alongside its benefits. The higher cost, limited parts ecosystem, and open-heart requirement make it less versatile than the NH35. However, for specific builds—particularly dress watches where the slim profile matters and the open-heart design is desired—the NH70 delivers features the NH35 cannot.
Ultimately, the NH70 isn't about being better or worse than the NH35. It's about serving different needs. The NH35 remains the default choice for most applications due to its unbeatable combination of cost, reliability, and compatibility. The NH70 serves those who specifically want its unique features and are willing to pay the premium for open-heart visual appeal, smoother sweep, and slimmer profile. Choose based on your priorities, and you'll be satisfied with either caliber.
0 comments
Leave a comment