Calendar cube thing

Roslyn and I were recently given a thing where you have cubes with numbers on to represent the date. The idea is that every day, you manually change the numbers displayed on the two 'dice', so that the number is between 01 and 31.

The geek in me glanced at the thing, and suddenly got curious about these two dice. If there's no geekness in you, then stop reading now, please. I just got curious about how the numbers were distributed between the two cubes. There were only two, which straight away told me that something clever must've been done.

A cube has six sides, and these were no different.

I could tell that clearly each cube needed the numbers 1 and 2, so that you can represent the 11th and the 22nd of any month.

As well as that, you need zero on both, because you can't have all of 1-9 on the 'other' cube.

So... we have 0,1,2 and three blanks on each cube. But we still have 3-9 to assign. That's seven numbers, in six spots. And here's the really nice bit, as to why that's okay...

Because you don't need both 6 AND 9, you just need one of them. :) Yeah, ok. I'm a big geek.