How to Regulate a Seiko NH35 / NH34 Movement

Why You’d Want to Regulate your NH35 / NH34 Movement

Improve Accuracy (The Main Reason)

Out of the factory, these movements are built to a wide tolerance:

• Roughly −35 to +45 seconds per day

That’s not because they’re bad—it’s because they’re designed for:

• Mass production

• Reliability over precision

👉 In real life, many run better than spec, but still:

• You might see +20 sec/day

• Or −15 sec/day

Regulating lets you bring that closer to something like:

• ±5–10 sec/day (very achievable)

  
  

1. What “Regulating” Actually Means

You’re not redesigning the movement—you’re simply adjusting how fast or slow it runs.

Inside the movement is a small lever called the regulator arm. Moving it:

• Toward “+” → makes the watch run faster

• Toward “–” → makes it run slower

This changes the effective length of the hairspring, which directly affects timing.

2. What You’ll Need

At minimum:

• Caseback opener

• Fine tool (toothpick or small screwdriver—non-magnetic preferred)

• Time reference (phone app or atomic clock)

Optional but highly recommended:

• Timegrapher (gives precise readings in seconds/day)

3. Step-by-Step Process

Step 1: Measure Your Watch First

Before touching anything, check how your watch is running:

• Compare it to an accurate time source over 24 hours

• Or use a timegrapher

👉 Example:

• +25 seconds/day → running fast

• −20 seconds/day → running slow

Step 2: Open the Caseback

• Use the correct caseback tool

• Be careful not to scratch the case

• Ensure the watch is clean and dust-free

You’ll now see the movement.

Step 3: Locate the Regulator

On NH35/NH34, look for:

• A small arm with “+” and “–” markings

• This sits on the balance assembly (the moving wheel oscillating back and forth)

There are actually two levers:

1. Regulator arm (what you adjust)

2. Beat error lever (DO NOT TOUCH unless you know what you’re doing)

👉 Only adjust the one marked + / –.

Step 4: Make Tiny Adjustments

This is the most important part.

• Move the regulator VERY slightly

• Think: fractions of a millimetre

Rule of thumb:

• Tiny movement = big change (10–30 seconds/day)

👉 Direction:

• Running fast → move toward “–”

• Running slow → move toward “+”

Use:

• A toothpick (safer, less chance of damage)

• Or a fine screwdriver (more precise, but riskier)

Step 5: Recheck Accuracy

After adjustment:

1. Close the caseback (you don’t need to fully tighten yet)

2. Wear the watch or let it run

3. Measure again over several hours (or use a timegrapher)

Repeat adjustments as needed.

4. Tips for Better Accuracy

Regulate in Real Conditions

Mechanical watches vary by position:

• Dial up

• Dial down

• Crown up/down

Try to regulate based on how you actually wear it.

Don’t Chase Perfection

NH movements are not chronometers.

Realistic goal:

• ±5 to ±15 seconds/day = very good

• ±20 seconds/day = normal

Let It Settle

After each adjustment:

• Give it time (a few hours to a day)

• Movements don’t stabilise instantly

5. Special Notes for NH34 (GMT)

Good news:

• The regulation process is identical to the NH35

The GMT complication:

• Does NOT affect regulation directly

• Only adds gearing for the extra hand

So treat it exactly the same when adjusting.

6. Common Mistakes to Avoid

1. Moving the Wrong Lever

The beat error lever is nearby—don’t touch it unless you understand beat adjustment.

2. Over-adjusting

Big movements = wildly inaccurate watch.

Always go tiny.

3. Magnetising the Movement

Avoid metal tools unless they’re anti-magnetic.

Magnetisation can cause:

• Huge time gain (minutes per day)

4. Dust or Moisture

Keep the movement clean:

• Work in a dry, dust-free space

• Don’t leave the case open too long

7. Advanced: Timegrapher Readings (Optional)

If you use a timegrapher, you’ll see:

• Rate (seconds/day)

• Amplitude

• Beat error

Focus mainly on:

• Rate for regulation

Ideal targets:

• Rate: close to 0 s/day

• Amplitude: 250–300° (healthy movement)

• Beat error: <1.0 ms (leave this unless trained)

8. Final Thought

The NH35 and NH34 are built for exactly this kind of adjustment. Unlike many less

capable movements, they’re:

• Forgiving

• Robust

• Beginner-friendly