In a distributed system, no hardware facilities exist to synchronise the clocks of the computers within the system. Algorithms designed to synchronise clocks in such systems have been the subject of much research. The lack of a global clock has meant that the accuracy of these algorithms has generally been assessed using indirect measures of clock offsets. We have developed a clock synchronisation test bed that allows for direct measurement of clock offsets. The test bed is now operational, and we have used it to produce initial results for the widely-used xntp package, and for some off-line synchronisation algorithms.