Watch accuracy calculator

How to measure properly

1. Use an accurate reference: time.is in your browser or a radio-controlled clock.
2. Read the offset without setting the watch, ideally when the reference seconds reach zero. Note it with its sign: +4 means 4 seconds ahead.
3. Take the second reading 24 hours or more later, at the same time of day.
4. Wear the watch as usual in between and leave it in the same position every night, for example dial up. Position changes the rate: for the NH3 movements TMI allows a difference of under 60 seconds per day between four vertical positions.
5. Repeat over several days. The average tells you more than a single day.

What is normal?

Time Module (TMI), the maker of these movements, specifies a static accuracy of −20 to +40 seconds per day for the NH35A, NH34A and NH38A. A watch that gains 10 seconds a day is therefore within range. The VK63A is a quartz-regulated chronograph movement; TMI specifies less than ±20 seconds per month.

TMI measures the movement statically: 10 to 60 minutes after full winding, in the dial-up, 9 o'clock-up and 6 o'clock-up positions, with the calendar not in function. On the wrist, position changes, state of wind and temperature add to that. That is why the average over several days counts.

When regulation is worth it

If the average over several days stays outside the manufacturer specification, or the rate changes suddenly, for example after a knock or near a magnet, take the watch to a watchmaker. They adjust the movement at the regulator. Do not open the case yourself.

Read on

• Guide: how to measure an automatic watch's daily rate
• Seiko movements compared by function
• The NH35 in mod watches
• Caring for a Seiko mod
• Contact form

Sources

• TMI Technical Guide Cal. NH3 Series (NH34A–NH39A), Version 03, 2025, retrieved 19 Oct 2026
• TMI Technical Guide Cal. VK6 Series (VK63A/67A), retrieved 19 Oct 2026
• Seiko FAQ: factors influencing the accuracy of mechanical watches, retrieved 19 Oct 2026