I heard this story on the radio last night, and I love it. It reminds me of an old Sufi 'Mullah Nasrudin' story:
Once, there was an old soldier whose job entailed firing a cannon from a hill top at six o'clock, every evening above a certain town.
He was renowned for the accuracy of his time-keeping, and after many years, they asked him how it was that he always managed to fire the cannon at dead on 6, despite not being able to afford a good pocket watch.
"I have never failed," he replied, "because every evening at 5. 45, I walk past the window of the clock-maker in town, and I check my poor watch with the excellent chronometer in his window. I then walk up the hill to the cannon and prepare it. At one minute to six, I approach the cannon and at six precisely, I fire it."
So they went to the old clock-maker in the town, and asked whether or not the chronometer in his window kept good time.
"Oh yes," he answered, "it is an excellent chronometer. For many years, every evening at six o'clock, a cannon is fired on the hill yonder, and I check the clock against it to see if it's right. It is always reading 6 o'clock precisely when the cannon is fired. That's how good this chronometer is."