A businessman has two cubes on his desk. Each cube has a number on each of its sides. Every day, the businessman arranges the cubes in such a way that the upward facing numbers display the day's date.
(Note that both cubes are always used for this, so on the 7th of the month, the cubes' surfaces display "07".)

How are these cubes numbered? (I.E. What numbers are on which cube? - call them C_{1} and C_{2}.)

(*From http://www.ocf.berkeley.edu/~wwu/riddles/intro.shtml*)