Charles Steinmetz, one of the most celebrated engineers of General Electric, was once called out of retirement by the management of General Electric to help it locate a problem in an intricate system of complex machines. Having spent some time tinkering with and testing various parts of the system, he finally placed a chalk-marked ‘X’ on a small component in one machine. GE’s engineers promptly examined the component, and were amazed to find the defect in the precise location of Steinmetz’s mark.

Some time later, GE received an invoice from the wily engineer - for $10,000. Incredulous, they protested the bill and challenged him to itemize it , asking him why he was demanding the amount for just a single chalk mark. Steinmetz did so : “Making one chalk mark: $1,” he wrote. “Knowing where to place it: $9,999.”