code: def extract_tendency_grid(self, model_grid):
          
          var_name = model_grid.variable + "-tendency"
          self.attributes[var_name] = []
          timesteps = np.arange(self.start_time, self.end_time + 1)
          for ti, t in enumerate(timesteps):
              t_index = t - model_grid.start_hour
              self.attributes[var_name].append(
                  model_grid.data[t_index, self.i[ti], self.j[ti]] - model_grid.data[t_index - 1, self.i[ti], self.j[ti]]
                  )
docs: Extracts the difference in model outputs
  
          Args:
              model_grid: ModelOutput or ModelGrid object.