From the developer: "Atomic Time Zone Server operates 5 Atomic Clock server services simultaneously and is the only time server in the world to do this. Outside synchronization of the server itself is done via other Atomic Clock Servers located in your own region. ATZ Server is built for reliable constant use in a server environment and can replace fully the Windows time services. ATZ Server provides atomically correct time to all it's requests and includes a 5 client license to use up to 5 ATZ Server Clients on other computers."