Errors

The indignant customer who receives an incorrect bill from a department store probably does not care what the source of the error was or even that, almost certainly, the fault was not a computer's but rather that of its data entry personnel or programmers. Neither is the astronaut who is descending toward the surface of the Moon very concerned about the precise source of the error that caused the onboard computer to fail. But an understanding of the sources of errors in computers is important to anyone who wishes to use or comprehend digital computers.