Regulating an NH35A automatic movement, a popular and reliable movement produced by Seiko, involves fine-tuning its timekeeping to ensure it maintains accuracy. The process requires precision, a steady hand, and specialized tools and a simple slip can render your hairspring bent or worse, requiring a repair. Regulation is recommended to be completed by a watchmaker.

NH35 Movement with Balance and Adjustments Shown

However, for educational purposes, here's a step-by-step walk-thru on regulating an NH35A movement:

Tools and Equipment Needed:

• Timegrapher

• Case back opener

• Watch holder

• Loupe or magnifying glass

• Fine-point tweezers

• Regulation tool or fine screwdriver

• Rodico or similar cleaning putty

• Dust blower/bulb

 Step-by-Step Review:

 1. Preparation

a. Work Environment: Ensure you are working in a clean, well-lit area free of dust and strong magnetic fields.

b. Gather Tools: Assemble all necessary tools and equipment within reach.

 2. Opening the Watch

a. Remove the Case Back: Use a case back opener to carefully unscrew the case back. Place the watch in a holder to keep it stable. It is common for untrained, and even trained repair technicians to mark up a case back when opening. Using a professional opening tool is highly recommended to avoid scratching your case back.

b. Secure the Watch: Secure the watch in the holder, ensuring that it is steady and will not move during the regulation process.

 3. Initial Assessment

a. Place on Timegrapher: Place the watch on the timegrapher in the dial-up position to get a baseline reading of its current rate, amplitude, and beat error.

b. Record Readings: Note the current timekeeping accuracy, amplitude, and beat error. The ideal beat error should be as close to 0 ms as possible.

 4. Adjusting the Beat Error (if necessary)

a. Locate the Regulator Assembly: Identify the regulator assembly on the NH35A movement, which includes the regulating arm and the balance wheel.

b. Adjust the Beat Error: If the beat error is significant, use a fine screwdriver to gently nudge the regulating arm in small increments. Check the timegrapher after each adjustment until the beat error is minimized.

 5. Regulating the Rate

a. Locate the Regulating Lever: Find the regulating lever which adjusts the rate of the watch. It is usually marked with a "+" and "-" or "F" (fast) and "S" (slow).

b. Adjust the Rate: Using a regulation tool or fine screwdriver, gently move the regulating lever towards "+" or "F" to make the watch run faster, and towards "-" or "S" to make it run slower.

c. Fine Adjustments: Make small adjustments and check the results on the timegrapher. Continue adjusting until the watch’s rate is as close to 0 seconds/day as possible.

 6. Checking Positions

a. Multiple Positions: Check the accuracy in multiple positions: dial up, dial down, crown up, crown down, crown left, and crown right.

b. Fine-Tune: If there are significant differences in rates across positions, make further fine adjustments to find a balance that minimizes deviation in all positions.

 7. Reassembling

a. Final Cleaning: Use Rodico or a similar cleaning putty to remove any dust or debris from the movement and case.

b. Close the Case Back: Carefully screw the case back on, ensuring it is tight to maintain water resistance.

 8. Final Testing

a. Monitor Over Time: Wear the watch or keep it on the timegrapher for 24-48 hours to monitor its accuracy and ensure stability.

b. Make Adjustments: If further adjustments are needed, repeat the fine-tuning process.

 Additional Tips:

- Patience: Regulation, and in fact all watch work, requires patience and precision. Avoid making large adjustments and if you are getting frustrated, take a break.

- Temperature Considerations: Be aware that temperature changes can affect the rate. If possible, regulate the watch in a controlled environment.

- Professional Help: If you are unsure or uncomfortable with the process, consider seeking help from a professional watchmaker.

Regulating an NH35A movement ensures your watch maintains its accuracy and reliability. But should be performed by a competent watchmaker. By understanding the factors that affect timekeeping and carefully following the regulation steps, you can enjoy the precision of your automatic watch for years to come. Regular maintenance and periodic checks will help keep your timepiece in optimal condition.

Barger Watch Company offers watches made with the Seiko NH series movements. Explore all of our watches here.