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  Because the Num Lock key's location on the keyboard makes it susceptible
  to inadvertent keystrokes, some programmers force the Num Lock toggle (bit
  5 of byte 0040:0017H) to a predetermined state at the beginning of a
  program. For example, clearing the Num Lock status bit before requesting
  user input from the keypad forces keypad keystrokes to be processed as
  direction keys instead of numbers, even if the Num Lock key was pressed
  accidentally. This can be particularly helpful with the 83-key keyboard
  for the IBM PC and PC/XT because this keyboard has no status LEDs and
  provides no visual indication of the Num Lock state.