OK, this is a little geeky. If you have a desktop computer that you know how to configure, or if you have a server that you administer, you can use the Letters Blogatory time service to set your computer’s clock!

Let me back up. Longtime readers know that I’m interested in the science of timekeeping. I wrote some posts about the proposed abolition of the leap second several years ago. I’ve also learned a bit about how networked computers synchronize their clocks, which is just as important, in this age of air travel and high-speed securities trading, as accurate watches were in the railroad age. Today, computers mostly use a protocol called the Network Time Protocol, or NTP, to keep their clocks in sync with UTC, or coordinated universal time. UTC, in turn, is derived from atomic clocks operated by national authorities (in the United States, the National Institute of Standards and Technology and the US Naval Observatory). In order to use NTP, you have to give your computer a list of servers to use as sources of time.

Since 2011, the Letters Blogatory web server has been an NTP client, obtaining time from other servers, but not providing time to any other servers. But for several months, I’ve been operating an NTP server, mostly for my own learning and as a way of donating some spare computing power to the public good. So you can now use time.lettersblogatory.com as one of the time servers you use to set your computer’s clock. Or, if you use the well-known “NTP pool” (pool.ntp.org) as a time server, there is a chance that you will be getting your time from the Letters Blogatory time server without really knowing it. Bear in mind that it’s not a good idea to use any one server as your source of time: you should use a list of several servers. Also, most of these time servers are operated by volunteers without any guarantees of accuracy or reliability, so if you are doing science or running a high-speed trading platform or something, you probably want to look into commercial alternatives.

My service may be particularly useful to folks in the Netherlands, as the server is located there, and as it’s a good idea to use time servers that can communicate with your computer with low latency, or in other words, without much lag. But any computer anywhere in the world can use the service. According to statistics the NTP pool publishes, it seems that I’m providing time to about 1.5% of the computers in the Netherlands using the pool!

How accurate is the Letters Blogatory time service? Take a look at these figures from the past week:

They show that the difference between my server’s clock and the clock of the server from which it’s obtaining time is never more than about 400μs (microseconds, or millionths of a second) and usually less than 200μs. And over any hour, the standard deviation of the offset is very small: over the past few days, it was generally less than 50μs. That’s pretty darn accurate!

There is one other cool feature of the service. NTP is one of the oldest internet protocols still in use, and it was not designed with security in mind. So there are various ways that bad guys can try to hack your computer by feeding it false time signals. The Letters Blogatory service uses Network Time Security, or NTS, which allows you optionally to get cryptographically authenticated time. Using NTS prevents such attacks.

Have fun!