I’ve always wondered why the snooze button on an alarm clock goes in nine minute intervals.  I was hoping for some psychological or physiological explanation (e.x. nine minutes was just “odd” enough that people wouldn’t get completely comfortable or something to that effect), but the real explanation is much more mundane.  It turns out that the first clock with a snooze button was a mechanical one and the gear configuration was such that they could either choose nine-plus minutes or ten-plus minutes (it wasn’t possible to make it exactly ten minutes).  They chose nine-plus because it was closer to ten minutes without going over.  When digital clocks came out it appears that the chip designers just copied the interval from the mechanical clocks, although with digital it was possible to make it precisely nine minutes.  And hence a standard was born.