What is the difference between Seiko/TMI/SII “NH” calibers?
As of this post there are 10 calibers in the current line of NH “Basic Mechanical Series” movements. We will focus on the main 6 variations based on the NH35, information about the other four will be at the bottom of the page.
There are some differences between these overall similar movements but they are all based off of the original NH35 caliber which is based off of the NH25. The differences are mostly related to day/date/24 hour indicator. Please compare in the chart below. Did we miss anything? Please comment below.
Time Module claims that the NH calibers are rated for static accuracy of -20 ~ +40 under normal temperature conditions. All measurements are done without the calendar function, as well as within 10-60 minutes while fully wound.
Difference Between Crown Functions
As we see here, the main differences between the two calibers is that the NH35A is hackable and can be hand-wound. That means the crown operates differently:
Unless the manufacturer installed a custom rotor, the caliber number should be engraved or stamped there. If it has a closed caseback or custom rotor, you can tell by looking at the complications on the dial. Of course, it’s always possible that the manufacturer made their own modifications or removed some features that didn’t correspond with the watch design (say for example they got a really good deal on 200 NH35A but the watch doesn’t have a date window, they could just use the NH35A without the date).
Which one better?
It really depends on what you need from a watch! If you like simple minimalist 3 hand watches, then the NH38A is for you. If you like have a 24 hour subdial, then go for a watch with the NH37A. Let the community know which caliber you prefer and why in the comments below…
Ladies and midsize NH calibers:
NH VS NE:
TMI aka Seiko Instruments markets the “NH” calibers as “Basic” Mechanical Series. They also have “NE” calibers that are marketed as “Premium” Mechanical Series.