code: def advance_to(self, timestamp):
          
          now = self.__original_time()
          if timestamp < now:
              raise ValueError("cannot retreat time reference: "
                               "target {} < now {}"
                               .format(timestamp, now))
          self.__delta = timestamp - now
docs: Advance the time reference so that now is the given timestamp.
  
          :param `float` timestamp: the new current timestamp.
          :raise `ValueError`: if *timestamp* is in the past.