After 12 years of hand-assembling custom timepieces and shipping to 12,868 buyers worldwide, I get asked the same question more than almost any other: what is the difference between the VK64 and the NH35?
It is a genuinely good question. Both movements power some of our most popular watches. Both are Japanese. Both are reliable. But they are fundamentally different types of movements designed for different buyers. Getting this wrong means buying the wrong watch — so I want to give you a straight answer based on 12 years of building with both.
What Is the NH35?
The NH35 is a 24-jewel automatic movement manufactured by Seiko Instruments Inc. (SII) — the movement division of Seiko. It has been in production for years and has earned a reputation as one of the most reliable automatic movements in its price class.
The defining characteristic of the NH35 is that it is self-winding. A rotor inside the case spins as your wrist moves throughout the day, winding the mainspring. You never touch a battery. The watch simply runs as long as you wear it.
Key facts about the NH35:
- 24 jewels — jewelled bearings throughout the movement to reduce friction and wear
- Hacking — when you pull the crown out to set the time, the second hand stops. This lets you synchronise to the exact second
- Hand-winding — you can also wind the watch manually by turning the crown
- Beat rate — 21,600 bph (6 beats per second)
- Power reserve — approximately 42 hours when fully wound
- Accuracy — typically ±10 seconds per day under normal wear
- No battery — ever
The NH35 is the movement inside our Vintage Milsub Mod, our Classic Vintage Edition, our JB Mod, and our SMP300 Homage. It is the movement that belongs inside a watch with military heritage, a rotating bezel, and a dial that respects the craft of traditional watchmaking.
What Is the VK64?
The VK64 is a completely different category of movement. It is a meca-quartz — a Japanese hybrid that combines a mechanical chronograph mechanism with a quartz oscillator for timekeeping.
The term meca-quartz stands for mechanical-quartz. The watch keeps time using a quartz crystal oscillator — the same technology used in any quartz watch — which means extraordinary accuracy. But the chronograph function (the stopwatch) is driven by a genuine mechanical mechanism with a physical pusher system.
The result is something unique: the smooth sweep of the central chronograph hand as it counts seconds, and the satisfying snap-back when you press the reset pusher. This is not the jerky tick of a typical quartz chronograph. It behaves exactly like a mechanical chronograph — because mechanically, it is one.
Key facts about the VK64:
- Quartz timekeeping — accuracy of ±15 seconds per month
- Mechanical chronograph action — genuine mechanical pushers, smooth sweep, clean snap-back
- Battery powered — requires an SR927W battery approximately every 3 years
- Two pushers — top pusher starts and stops the chronograph, bottom pusher resets to zero
- Sub-dial at 6 o'clock — shows the running seconds at all times
- Large central hand — the stopwatch hand only. Does not move unless the chronograph is active
- No hacking — the second hand continues running while you set the time
The VK64 powers our Blue Speed Mod, our Ice Gold Speed, and our Silver Tiffany Mod. It is the movement that belongs inside a watch with a bold dial, a chronograph complication, and an electric character that commands attention.
The Core Difference: Automatic vs Meca-Quartz
This is the fundamental question, and it comes down to what you value most in a watch.
If you want a watch that never needs a battery, the NH35 is your movement. There is something deeply satisfying about a mechanical watch that powers itself from your movement. Wind it once, wear it daily, and it runs indefinitely. This connects you to 150 years of watchmaking tradition.
If you want a watch with a functioning chronograph, the VK64 is your movement. A genuine automatic chronograph at this price point would cost ten times what we charge. The VK64 delivers the mechanical action and aesthetic of a chronograph with quartz accuracy for everyday timekeeping.
These are not competing movements. They are different tools for different purposes.
Accuracy: How Much Does It Matter?
The NH35 is accurate to approximately ±10 seconds per day under typical wearing conditions. Over a month that is potentially 5 minutes of drift. For most people this is completely acceptable — you set it once a week and it is fine.
The VK64 is accurate to approximately ±15 seconds per month. Over a year that is around 3 minutes of drift. For daily timekeeping this is essentially perfect.
If precision timekeeping is critical to you, the VK64 wins on accuracy. If you simply want a reliable everyday watch and don't mind a minor weekly adjustment, the NH35 is more than adequate.
The Chronograph Question
This is where the choice becomes clearest. If you want a watch with sub-dials, pushers, and the ability to time events — you need the VK64. The NH35 does not have a chronograph complication. It is a time-only movement.
The VK64 chronograph works like this: press the top pusher and the large central sweep hand begins moving, counting elapsed seconds. Press it again to stop. Press the bottom pusher to reset. The 30-minute counter sub-dial at 3 o'clock tracks minutes. The hour counter at 9 o'clock tracks hours.
One thing that confuses new VK64 owners: the large central hand does not show regular seconds. The running seconds are shown by the small sub-dial at 6 o'clock. The large hand only activates when you start the chronograph.
This is not a fault. It is how all chronograph watches work. But it surprises people who expect the large hand to be ticking constantly.
Which Movement Is Right for Which Buyer?
Over 12 years and 12,868 customers, I have noticed clear patterns in who chooses which movement.
The NH35 buyer typically:
- Values the mechanical tradition of automatic watchmaking
- Wants a watch that works without a battery forever
- Appreciates military or heritage watch aesthetics
- Prefers understated dials without too many complications
- Is drawn to the Milsub, Classic Vintage, or GMT range
The VK64 buyer typically:
- Wants a bold dial with visible chronograph complications
- Values the stopwatch function for sport or daily timing
- Does not mind replacing a battery every 3 years
- Is attracted to the motorsport and speed-inspired aesthetic
- Is drawn to the Blue Speed, Ice Gold, or Silver Tiffany
Neither is the right answer for everyone. Both are the right answer for the right person.
Water Resistance
Both movements are housed in cases rated to at least 50 metres water resistance. The water resistance is a function of the case construction — not the movement itself.
With both watches, always ensure the crown is screwed down before water exposure. With the VK64 specifically, never press the chronograph pushers underwater. Pressing them creates a pathway for water to enter the case around the pusher seals.
Servicing and Long-Term Ownership
The NH35 requires periodic servicing — ideally every 3 to 5 years — which involves cleaning, lubrication, and inspection. The cost is typically $50 to $150 at a qualified watchmaker.
The VK64 requires a battery replacement approximately every 3 years. This costs $5 to $15 at any watch repair shop. After battery replacement, we recommend having water resistance retested before exposing the watch to water.
In terms of long-term cost, both movements are affordable to maintain.
A Note on the VK63
You may see references to the VK63 in our product range. The VK63 is the sister movement to the VK64 — functionally identical in how it operates, with minor internal differences in the gear train. For all practical purposes as a watch wearer, the VK63 and VK64 behave identically.
The VK64 powers the Blue Speed and Ice Gold. The VK63 powers the Orange Speed, Silver Black, Green Mod, and Yellow Speed.
The Verdict
Choose the NH35 if:
- You want a watch with no battery dependency ever
- You value the heritage of mechanical watchmaking
- You prefer a cleaner dial without chronograph sub-dials
- You are buying the Milsub, Classic Vintage, JB Mod, or GMT range
Choose the VK64 or VK63 if:
- You want a functioning stopwatch chronograph
- You want a bold, busy dial with multiple sub-dials
- You accept a battery replacement every 3 years
- You are buying the Blue Speed, Ice Gold, Orange Speed, or Yellow Speed
There is no wrong choice. Every watch we build is hand-assembled and individually inspected before it ships. Both movements are Japanese, both are reliable, and both are backed by our 180-day international warranty.
The question is simply: what kind of watch buyer are you?
Kevin has been founding and building ZJani Mods for 12 years. The full collection of NH35 and VK-powered watches is available at zjani-mods.com. Every piece ships with a 180-day warranty, 30-day returns, and free insured shipping.
