The NH Series from Seiko is a line of movements derived from the Seiko 4R.. calibers. Both are manufactured by Time Module (TMI). The key difference lies in their intended use and features: The 4R.. caliber is Seiko’s proprietary caliber for its own watches, while the NH.. calibers are licensed to third-party manufacturers.
The NH Series (e.g., NH35, NH36, NH38, NH71) is considered a robust and reliable workhorse that forms the foundation of the modern micro-brand trend.