[CentOS] System Time Source

[John Hodrien]

On Wed, 24 May 2017, Pete Biggs wrote:

> The GPS time system is also notoriously very precisely wrong. The time
> was set when the first satellite was sent up and has never been
> corrected since - so hasn't taken account of leap seconds or
> relativistic effects. All that matters for GPS is that the time on each
> satellite transmission is identical, and to that end you can get a
> precision of about 3ns (which is what you need to get metre GPS
> accuracy) and which you then have to correct for all the various
> artefacts since inception. Lower cost GPS receivers get about 50ns
> accuracy, which is probably still OK for a system clock. The good thing
> is that the corrections necessary are well known and updated
> frequently.

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
https://www.aapt.org/doorway/TGRU/articles/Ashbyarticle.pdf
http://www.timetoolsglobal.com/information/gps-ntp-server/

I'll accept that it doesn't include leap seconds, but it does provide the
offset from GPS time to UTC, so that's not an issue.

I understand the exact opposite as far as relativistic effects, with
countering them being necessary for it to work as a positioning system.

jh