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