Just a sec'!
Historically, mankind measured time by the passing of the days. But the length of a day varies as the Earth wobbles on its axis. Eventually, in the 1960s, atomic clocks were developed that were stable enough to depend upon, and accurate enough to lose one second only every 100 million years. These clocks are the basis for defining a second and international time co-ordination.
But one second in 100 million years? That seems rather sloppy, wouldn't you agree? So French researchers have developed optical lattice clocks that are far more careful with such a precious commodity as time, and will lose one second only every 300 million years.
Even that isn't really good enough for those of us who truly treasure promptness. I'm eager for the ion clock to become more stable and widespread, so we'll lose one second only every few billion years…give or take a few seconds.