A man is strolling past a university and suddenly remembers he has an important meeting that afternoon.
Unfortunately, his watch has stopped, and he cannot tell if he is late or not. Then, he notices a young student strolling nearby.
Calling out to the student, the man says, “Pardon me, sir, but do you have the time?”
The student calls back, “One moment!” and throws himself upon the ground, pulling out a short stick as he does. He pushes the stick into the ground, and, pulling out a carpenter’s level, assures himself that the stick is vertical.
With a compass, the student locates north and, with a steel ruler, measures the length of the stick’s shadow.
Withdrawing a slide rule from his pocket, the student calculates rapidly, then swiftly packs up all his tools and turns back to the man, saying, “It is now precisely 3:29pm.”
The man can’t help but be impressed by this demonstration, and says to the young student, “That was really quite remarkable.”
As he starts to walk away, he asks, “What do you do on a cloudy day, or at night, when the stick casts no shadow?”
The student holds up his wrist and says, “I suppose I’d just look at my watch.”