Pick one and press Start, then click Next › to step through it.
Each sync snapping a clock close to the source but not exactly onto it — the leftover gap is the round-trip uncertainty.
Why there's no perfect shared 'now' across machines, and what a sync protocol can and can't fix.
Clocks tick at slightly different rates, so they DRIFT apart. SYNC asks the time source and corrects, but the network round-trip means the answer is already a little stale — leaving a residual skew bounded by the RTT.