The correct answer is: A. is a method for controlling the operation of a machine by means of a set of instructions.
Numerical control (NC) is the automation of machine tools that are operated by a computer. In modern NC systems, the computer is programmed using a computer-aided manufacturing (CAM) software package. The instructions in the program are called a “part program” and they tell the machine how to move the cutting tool to create the desired shape of the part.
NC machines are used to manufacture a wide variety of products, including machine tools, aircraft parts, medical devices, and automotive components. They are typically more accurate and efficient than manually operated machines.
Option B is incorrect because NC can be used to control a wide variety of machines, not just milling machines. Option C is incorrect because NC is not a method for producing an exact number of parts per hour. The number of parts produced per hour depends on the complexity of the part and the speed of the machine. Option D is incorrect because not all NC machines are programmed using a computer. Some older NC machines were programmed using punched paper tape. Option E is incorrect because NC is a real and useful technology that is used to manufacture a wide variety of products.