Chrony is a versatile implementation of the Network Time Protocol (NTP). It can synchronise the system clock with Network Time Protocol servers, reference clocks (e.g. GPS receiver), and manual input using wristwatch and keyboard. It can also operate as a Network Time Protocol version 4 (RFC 5905) server and peer to provide a time service to other computers in the network. It is designed to perform well in a wide range of conditions.

https://chrony.tuxfamily.org

NTP is intended to synchronize all participating computers to within a few milliseconds of Coordinated Universal Time. It uses the intersection algorithm, a modified version of Marzullo's algorithm, to select accurate time servers and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy.

https://wikipedia.org

The NTP model includes a number of widely accessible primary time servers synchronized by wire or radio to national standards. The purpose of the NTP protocol is to convey timekeeping information from these primary servers to secondary time servers and clients via both private networks and the public Internet. Precisely tuned algorithms mitigate errors that may result from network disruptions, server failures, and possible hostile actions.

IETF RFC5905