[lutorm]

Time measurements are interestingly difficult when you start to care about high accuracy or long times. There's a kind of hard-to-read but interesting running log on the state of the leap second at http://www.ucolick.org/~sla/leapsecs/onlinebib.html. (What, you didn't know there were leap seconds? See http://en.wikipedia.org/wiki/Leap_second)