Most of the time we each glance at a watch or clock and are happy to use the approximate time we see there. Rarely are we concerned about the exact time in our daily lives. Computers though are very different! If machines can't agree what time it is then our emails could appear to arrive before they've left! And maintaining a comparative log of what happens across a group of machines becomes impossible if they don't agree what time it is.
To solve this problem, NTP - The Network Time Protocol - was created in 2003. Sources such as atomic clocks are then used to distribute the time around the internet and are known as "stratum 1" because they are directly connected to such reference sources and are therefore at the 'top' of the time server organisation.
Other time servers then receive the time from servers 'above' them in the heirarchy, so a stratum 2 time server receives the time from one or more stratum 1 time servers. A "Stratum 2" time server isn't significantly less accurate than a stratum 1 time server, indeed even a "stratum 10" keeps accurate time for the vast majority of uses.
Because there seemed to be few high-quality time servers currently available in the UK I created ntp.markyate.net as a stratum 2 network time source, and its availability has been donated to the UK ntp pool. It is available via both IPv4 [18.104.22.168] and IPv6 [2001:4d48:ad51:2b03::da7e] but this is taken care of for you automatically when you use the pool. One day we hope to slightly refine the timekeeping by upgrading ntp.markyate.net to a 'Stratum 1' server by using direct reception of the GPS signal, which is accurate to approx. 14 nanoseconds and uses an atomic clock, however we've been planning to do this for some years now so don't hold your ... breath.
This timeserver runs on a dedicated machine; other than a couple of web pages (including this one) it does nothing else except maintain and distribute very accurate time. Previously this was a Sun SunFire v100 running FreeBSD but currently -- temporarily -- this is on a Raspberry Pi due to network reconfiguration. The status of the server is monitored separately for each access address. Note that servers are monitored from California, USA. As a single machine serves both IPv4 and IPv6 time transatlantic network issues will regularly give rise to apparent delays and failures in the service due to transatlantic congestion and any difference in the graphs will reflect that.
Although available world-wide, this time server is primarily intended for use by UK and European users.
The green dots signify the time difference registered between the remote monitoring server and the local monitored server. It is measured in milliseconds (1/1000ths) on the left-hand scale. Ideally the green dots should fall within a narrow horizontal band.
The blue line and right-hand scale provide a estimate of the 'quality' of the time server, where a score of twenty is the maximum. If the score is below 10 the server concerned is removed from the pool temporarily.
"The Pool" is, indeed, the best way to get your time check as it automatically ensures that you get use of an accurate time source without the possibility of the network link to an individual server going down. As such if you are using NTP to set your own machines' clocks then use of the pool is your solution. Information on using it can be found at http://www.pool.ntp.org/. There are currently 4343† time servers which are members of the pool world-wide, many volunteered and operated pro bono by individuals as a service to others.
If you have a suitable machine connected permanently to the internet and with a fixed IP address then please consider making it available to others too. If you wish to use ntp.markyate.net as one of your up-stream servers on a permanent basis then refer to NTP support for the requirements and ensure you advise firstname.lastname@example.org before commencing use, otherwise you are liable to be marked as an abusive server and blocked!