Six Milliseconds Of Drift

Spanner's TrueTime returns an interval whose half-width is the uncertainty $\epsilon$. Two components make it up: local clock drift accumulated since the last sync with a time master, plus the round-trip uncertainty of talking to that master. In the paper's production setting the applied drift rate is $200\ \mu s/s$, the daemon polls a time master every $30$ s, and the communication term contributes about $1$ ms.

A proposal lands to cut poll traffic by moving the interval from $30$ s to $120$ s. Compute the worst-case $\epsilon$ before and after.