You don't need a timepiece because your phone has a clock, but if you're going to wear one anyway, you should have it make a statement. Here's what this Casio Databank calculator watch says: I'm retro, I'm nerdy, and I think math is really important.
Casio's CA53W watch manages to be both retro and futuristic at the same time. Maybe that's why Marty McFly rocked it in Back to the Future and pretty much every single 80s kid wore one to school. Just look at it: 16 buttons, which allow you to add, subtract, divide and multiply to your heart's content. And as a Casio quartz watch, it'll tell the time quite reliably.