anchor.diff:  -define(PWM_RIGHT, 11).
   -define(DIR_LEFT, 12).
   -define(DIR_RIGHT, 13).
  --define(SLEEP, 10).
  +-define(SLEEP, 20).
   -define(STOP_SLEEP, 30).
   -define(TEST_SLEEP, 3000).
   -define(CHANGE_SLEEP, 500).
  
positive.code:             ok;
          Value when Value =< ?THRESHOLD andalso PrevDistance > ?THRESHOLD ->
              stop(forward),
              rotate(left)
      end,
      timer:sleep(?SLEEP),
  
negative.code:         Value when Value > ?THRESHOLD andalso PrevDistance =< ?THRESHOLD ->
              timer:sleep(?CHANGE_SLEEP),
              stop(rotate_left),
              timer:sleep(?CHANGE_SLEEP),
              forward();
          Value when Value > ?THRESHOLD andalso PrevDistance > ?THRESHOLD ->
              % maintain course
  