It's used to calculate and calibrate the official precise time duration of one "second", but who needs Caesium-133 when you can just run?
I've run 3 times this week, best guess 6 miles each time, 2 different routes around the neighborhood, and the 3rd route a brand new one in a completely new direction that I've never done before. There's almost absolutely nothing similar in these routes: different time of day, different number of intersections, traffic, waiting at stop lights etc. Each time when I got home, here's my time:
Weird or what?