@InProceedings{Lenzen2009Tight,
	 author =	{Christoph Lenzen and Thomas Locher and Roger Wattenhofer},
	 title =	{{Tight Bounds for Clock Synchronization}},
	 booktitle =	{{28th ACM Symposium on Principles of Distributed Computing (PODC), Calgary, Canada}},
	 month =	{August},
	 year =		{2009}
}