The WebTimer service is traceable to UTC(AUS), the Australian realisation of Co-ordinated Universal Time (UTC). UTC(AUS) is the legal reference for time and frequency in Australia and is the output of a caesium atomic clock operated at the National Measurement Institute's Lindfield laboratory in Sydney.

Atomic clocks at NMI
Atomic clocks at the NMI Lindfield laboratory

The WebTimer server is directly synchronized by the 1 pulse-per-second output of UTC(AUS). Any residual difference between the server time and UTC(AUS) is measured and recorded; this difference is no more than a few tens of microseconds.

For a technical description of the traceability chain, including the uncertainty budget, please read this document.