Cal. 9S55 is an automatic movement with date produced by Shizukuishi Watch Studio for Grand Seiko. Launched in 1998, it was the first modern Grand Seiko mechanical movement and the basis for the Grand Seiko 9S5x movement family. It is a modern movement operating at 8 Hz (28,800 A/h) and is accurate ti -3/+5 seconds per day. Cal. 9S55 was phased out in favor of Cal. 9S65 in 2010.
Cal. 9S55 was based on the design of Cal. 4S35, the first modern high-end mechanical movement from Seiko. That movement, in turn, was developed from the design of the 1970 Cal. 5206, which had been retired in the 1970s and revived in 1992.
| Production | Application | Winding | Jewels | Notes | |
|---|---|---|---|---|---|
| 8L21 | 2003-2007 | Brightz SAGL | Automatic | 24 | Similar to 9S51 |
| 8L34 | 2000 | Railway pocket watch | Manual | 20 | Small seconds |
| 8L35 | 2000-present | Brightz SAGQ Prospex SBDX Prospex SLA | Automatic | 26 | Date, similar to 9S55 |
| 8L36 | 2011-present | Credor GCBZ Galante SBLM | Automatic | 27 | GMT, similar to 9S56 |
| 8L38 | 2010-2015 | Galante SBLL | Automatic | 26 | Open Heart |
| 8L75 | -2005 | Credor GCBR | Automatic | 26 | Date, similar to 9S55 |
| 9S51 | 1998-2009 | GS SBGR | Automatic | 24 | No date |
| 9S54 | 2001-2010 | GS SBGW | Manual | 20 | No date |
| 9S55 | 1998-2010 | GS SBGR | Automatic | 26 | Date |
| 9S56 | 2002-2010 | GS SBGM | Automatic | 27 | GMT, no date |