Unfortunately the calibre character is shared between calibre families. For example B is shared between the 5X GPS Solar calibres, and the 4R automatic calibres. While this is not currently an issue as Astron is the only collection to use the 5X calibre family under the new scheme, and you would not get a 4R mechanical Astron, it could cause an issue in the future. If a 5X GPS solar calibre was used in a future Prospex watch, the model number would begin with HBB, the same prefix as used with 4R based Prospex’s.
Currently other calibre families that share the same model prefix character are divided between Collections. For example, C calibre families are both 7B and 6R movements, but the 7B has only been used on Astron & Lukia models, and the 6R has only been used on Prospex and Presage models. For the D calibre families, the 8B has only been used for Astron models, and the 8R has only been used for Prospex models.
It would have been clearer and easier to understand if each calibre family was allocated a unique character so people could easily determine the calibre family directly instead of having to also consider the Collection. Thai would also have eliminated any future confusion if calibre families were expanded into other collections.
The model number is completed with three digits. These numbers no longer appear to have any specific meaning and are likely allocated sequentially as products are designed. On the older system the digits were even numbers for models with non silver colored bezels, e.g. gold or rose gold bezels, but this is no longer the case and the bezel coloring can not be determined from the numbering.
Seiko model numbers have begun with the letter S since the mid-1980’s, so it is a shock for some fans of the brand when looking at the new numbers, but I am sure this is something that people will get used to.
