code: def mean_alnt_target_distance(self, data_frame):
          
          dist = np.sqrt((data_frame.x[1:-1].values-data_frame.x[0:-2].values)**2+
                         (data_frame.y[1:-1].values-data_frame.y[0:-2].values)**2)
          matd = np.mean(dist[np.arange(1,len(dist),2)])
          duration = math.ceil(data_frame.td[-1])
          return matd, duration
docs: This method calculates the distance (number of pixels) between alternate tapping
  
              :param data_frame: the data frame
              :type data_frame: pandas.DataFrame
              :return matd: the mean alternate target distance in pixels
              :rtype matd: float