A time keeper at a factory is in charge of blowing the whistle for the lunch break at noon. When it's almost noon she looks at her watch and right when it strikes 12pm she blows the whistle.
One day she bumps her watch against something and she fears that it is a little off.
Wanting to make sure that she can do her job correctly she decides to go get her watch set by a professional clock maker.
The woman goes to the shop and has the clock maker set her watch to the correct time. She tells the clock maker what she does for a living and that it is important that her watch keeps correct time.
The clock maker tells her that she needn't worry because he set his watch by the clocks in the back and that he can be sure that they're on time because he sets them every Sunday when the church bells ring at 6am.
The woman leaves the shop satisfied... but starts to ask herself... "How does the church know exactly when it is 6am?"
So she goes to the church and finds the bell ringer and asks him how does he know when to ring the bells and how does he make sure that he has the correct time.
The bell ringer tells her that he rings the bells right when his watch strikes 6am. "I'm sure my watch is accurate." He reassures her. "I check it every day at noon when the factory goes on break."