The millisecond-scale operation of an analog on-off switch is an eternity to a computer. Does that tremulous signal mean a finger meant to push the button once or twice? Is the computer being misled by microvoltages created by electronic interference? Did a user really push the button at all?

As one authority puts it, "Switches can do some really odd things. . . . Switches don't make and break cleanly on the time scales of digital systems."

Thus...