High accuracy time synchronization is needed for devices like cardiology equipment. The measurements taken on various different machines are recorded with synchronization modules specifying the precise time base for measurements such as waveforms and multi-frame images. These are later used to synchronize data for analysis and display.
Typical requirements are:
Synchronized to within approximately 10 millisecond. This corresponds to a few percent of a typical heartbeat. Under some circumstances, the requirements may be stricter than this.
Time base stability
During the measurement period there should be no discontinuities greater than a few milliseconds. The time base rate should be within 0.01% of standard time rate.
International Time Synchronization
There are no special extra requirements. Note however that time base stability conflicts with time synchronization when UTC time jumps (e.g. leap seconds).