Seiko's nomenclature can be quite confusing (the 
link watch names tend to sound like second-tier Star Wars droids), but the enthusiast fanbase makes it easier to understand by 
link bestowing nicknames. The SPB207, for instance, falls under the "MM200" moniker because it's a "baby" version of the MM300. (The 
link "200" and "300" come from the water resistance rating.)