[ That Nier comes from a world where technological advancements aren't commonplace beyond an old, abandoned factory doesn't cross 9S' mind at all, so he can only wonder: how complicated could it be? That thought aside, he does oblige: ]

Well, androids are built for different reasons, right? [ Just dropping that particular tidbit here, because if he's asking, Nier has to know, wouldn't he? ] So a model number lets you know what kind of build they have and the purpose they serve—but that goes for a lot of other things, too.