A repairman was hired to repair a large machine in a factory.

He showed up, examined the machine, then tapped it once with a hammer. It started up. The factory owner was pleased, but not when he got a bill from the repairman for $100. He thought that was outrageous, and he asked for an itemized bill. So the repairman handed him a bill which said: Tapping machine with hammer: $1 Knowing where to tap: $99