Seiko Cal. 6R21 is a midrange automatic movement produced by Seiko Instruments Inc. (SII) for Seiko watches. Since 2010, it is also sold by Time Module Inc. (TMI) as Cal. NE20 (or NE20B) for use by other manufacturers. Like other Seiko 6R movements, it is more refined and accurate than the related Seiko 4R series and uses a Spron 510 mainspring. Unlike Cal. 6R15, it is a “Hi-Beat” movement operating at 28,800 A/h and has complications: Subdial day by pointer at 3:00, subdial date by pointer at 6:00, and counter-clockwise power reserve at 9:00.
Cal. 6R21 was introduced around 2009 and remains in production today. It has 29 jewels and 208 parts. Cal. 6R21 was used in the Ananta Multi-Hand Automatic watches, models SPB017J1, SPB019J1, and SPB021J1, produced August 2009 through March 2013.
According to Seiko documents, this is a modular movement based on Cal. 6R15 but with a Hi-Beat balance and hacking seconds. Cal. 6R20 is similar but has a clockwise power reserve indicator at 9:30.
Seiko 6R21 Applications
Cal. 6R21 is a rare movement found in only one model as of 2020.
- Seiko Presage SPB085
| Jewels | Components | Speed | Power | 3:00 | 6:00 | 9:00 | |
| 6R15 | 23 | 168 | 21,600 | 50 | Date Window | ||
| 6R20 | 29 | 208 | 28,800 | 45 | Day Subdial | Date Subdial | Clockwise Power Reserve |
| 6R21 | 29 | 208 | 28,800 | 45 | Day Subdial | Date Subdial | Counter-Clockwise Power Reserve |
| 6R24 | 31 | 224 | 28,800 | 45 | Retrograde Day | Retrograde Date | Clockwise Power Reserve |
| 6R27 | 29 | 28,800 | 45 | Date Subdial | Counter-Clockwise Power Reserve | ||
| 6R35 | 24 | 21,600 | 70 | Date Window |