ITC is never synchronized between cpus. On some systems all processor ITC may be driven from the same clock ... so an "offset from absolute system time" would work on those systems. But on others the ITC on different processors may be driven from different crystals, so the *rate* may be different. The difference may be small if the crystals have the same nominal frequency, but in the worst case the rates may be readically different (e.g. in some SGI systems ~1.2GHz on some cpus and ~1.6GHz on others).

-Tony