Computers started counting time on January 1st, 1970, and added one second-per-second. If your clock shows you're in the 70's, it's reset to the start.
Servers which take their time from an observatory we call Stratum 1 servers. Servers which takes their time from Stratum n servers are Stratum n+1 servers.
Install ntp with:
> sudo apt-get install -y ntp
The shell command for this is `ntpq`. Monitor the service providers using: