code: def best_units(self, sequence):
          
          # Read
          #   [(0.9, 's'),
          #    (9, 'm)]
          # as, break ranges between 0.9 seconds (inclusive)
          # and 9 minutes are represented in seconds. And so on.
          ts_range = self.value(max(sequence)) - self.value(min(sequence))
          package = self.determine_package(sequence[0])
          if package == 'pandas':
              cuts = [
                  (0.9, 'us'),
                  (0.9, 'ms'),
                  (0.9, 's'),
                  (9, 'm'),
                  (6, 'h'),
                  (4, 'd'),
                  (4, 'w'),
                  (4, 'M'),
                  (3, 'y')]
              denomination = NANOSECONDS
              base_units = 'ns'
          else:
              cuts = [
                  (0.9, 's'),
                  (9, 'm'),
                  (6, 'h'),
                  (4, 'd'),
                  (4, 'w'),
                  (4, 'M'),
                  (3, 'y')]
              denomination = SECONDS
              base_units = 'ms'
  
          for size, units in reversed(cuts):
              if ts_range >= size*denomination[units]:
                  return units
  
          return base_units
docs: Determine good units for representing a sequence of timedeltas