The number also indicates the material that the bezel is made from. The second part of a model number is a unique three digit number that identifies a model within the series. Presumably if Grand Seiko were to introduce a new automatic Spring Drive calibre that featured a date, chronograph, and GMT complications these would be released under a new SLGC series. The SBGH and SLGH series both feature Hi-Beat automatic movements with a date complication. These new series align with the previous ranges with both the SBGA and SLGA series featuring Spring Drive automatic movements with date and power reserve. In 2020 two new calibres, and consequently new series, were introduced with the SLGA and SLGH. The characters Q, O, U, and I were avoided to avoid confusion with 0, V, and 1. Eventually almost all characters were utilized, with a few characters skipped to avoid confusion.

Date,, Ĭonstant Force Tourbillon, Deadbeat Seconds, Power ReserveĪs the calibre types expanded additional series were added with the last character in the four changing, e.g.

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