This weekend Joshua asked me if he could play a computer math game, and we settled on multiplication 1-12. That made me wonder...why do we learn through 12 by heart? That's a weird number. Why not 10? Or 15?
My guess was clocks.
The internet was helpful! Well, mostly helpful. The first result helpfully reminded me that multiplication tables don't stop at 12 but go through infinity. It went on to say that there used to be 12 pence in a shilling in England, so to do any shopping you needed to know through your x12 well.
As I'm thinking about this, I realize I use my x12 fairly often. Sometimes converting between hours and days, sometimes between inches and feet. So I guess it's still important to have them memorized.