A common configuration for FSMLabs TimeKeeper customers is to cross-couple time sources in New Jersey and New York City or London and Slough or Chicago and Aurora or Singapore and Sidney - any two trading locations that are connected with high quality network. Sometimes the network connection does not even have to be that great. TimeKeeper will cross-check time sources, complain when things look wrong, and failover when needed. Multiple time sources also produces a timestamp provenance. Trading applications will have a record showing that the timestamps they produce were in agreement with two or more independent sources. A number of firms scale this basic design to multiple sites: increasing the depth of fault-tolerance and the strength of the provenance. Cross-coupling time feeds also provides early warning on a number of network problems. Several customers saw TimeKeeper warnings about secondary sync and found on investigation that their network providers were changing equipment or rerouting without notice.