def fix_timestamps(self, time_ref):
		"""
			manipulates internal time stamps such that the last run ends at time 0
		"""
		
		for k,v in self.data.items():
			for kk, vv in v.time_stamps.items():
				for kkk,vvv in vv.items():
					self.data[k].time_stamps[kk][kkk] += time_ref
manipulates internal time stamps such that the last run ends at time 0