@topsecret Another option is to run a hardware network time server which uses an atomic clock. Then point the NTP client for the systems of your client at that hardware time server.
You can choose one of the following hardware time servers:-
https://www.microchip.com/en-us/products/clock-and-timing/systems/enterprise-network-time-servers/syncserver-s600 https://timetoolsltd.com/products/network-time-server-appliances/ https://www.oscilloquartz.com/en/products-and-services/ntp-servers https://chronos.uk/products/sync-timing/ https://safran-navigation-timing.com/solution/timing-and-synchronization/For clients which can't have internet at all even for NTP time synchronisation then running a hardware time server is a must for the network. That way all of the clocks will then be in sync with each other.
