Cristian's algorithm (introduced by Flaviu Cristian in 1989)[1] is a method for clock synchronization which can be used in many fields of distributive computer science but is primarily used in low-latency intranets.
Cristian observed that this simple algorithm is probabilistic, in that it only achieves synchronization if the round-trip time (RTT) of the request is short compared to required accuracy.
It also suffers in implementations using a single server, making it unsuitable for many distributive applications where redundancy may be crucial.
Put simply: If the RTT is actually split equally between request and response, the synchronisation is error-free.
Offset and jitter of the synchronisation are thus minimised by selecting suitable RTT from a set of many request/response pairs.