Chronyd is a background program, and Chronyc is a command line interface to it.
Time reference sources for Chronyd can be RFC1305 NTP servers, humans using the keyboard and Chronyc, and the computer's real-time clock at boot time.
Chronyd can determine the rate at which the computer gains or loses time and compensate for it while no external reference is present.
Chronyd's use of NTP servers can be switched on and off through Chronyc, to support computers with dial-up/intermittent access to the Internet.
Chronyd can also act as an RFC1305-compatible NTP server.