[grandsham]

The way that the author uses GPS to get time (NMEA messages) works well for the purposes of the article, eg syncing a wristwatch to ~1 second accuracy. As another poster pointed out though, these messages are only accurate to about a half-step one, and it is actually worse than just using an internet NTP signal.

If you want to build a GPS based NTP server, you need a GPS board that outputs a PPS signal. When I built mine I used an adafruit board hooked up to a raspberry Pi's GPIO pins.

It's something of a bear to get everything to play together properly and get the extremely precise PPS signal to the NTP server, I recall it required a custom kernel module and a lot of tinkering with tick rates.

[gonzo]

I watched (and guided, some), my son do this in his summer between high school and college.

http://store.netgate.com/Lures/GPS.aspx