On Fri, 22 Jul 2016 07:53:22 +0100, "Brian Gaff"
wrote:

However, I often have a laugh at the difference in time between radio
controlled clock, DAB clock and the internet bassed one on the pc.
Several seconds quite often. Who is right?

The DAB clock display should be accurate as it uses a separate data
stream. However, while some receivers show accurate time others
appear to be out by a fixed amount which can be 5-10 seconds adrift.

The separate GMT audio hour "pips" are not accurate on DAB as the
processing delay can be 2-8 seconds.

The radio controlled clock will synchronise with the time reference
(DCF or MSF) once or twice a day, usually at midday/midnight plus or
minus 1 hour. In between these times it relies upon its own internal
clock but shouldn't be out by more than a fraction of a second.

PC internal clocks are (by timekeeping standards) very inaccurate. PC
clock can drift by seconds a day. Modern versions of windows can
synchronise with a time server but by default only do it once a week.
(You can't easily alter this either) so can be out by 10's of seconds.
Using the free Meinberg NNTP software
https://www.meinbergglobal.com/english/sw/ntp.htm you can alter the
synchronisation interval to any time.

Time shown on any GPS device will usually be accurate.

So who is right comes down to GPS - always, Radio Controlled clock -
usually to within less than a second, DAB - display - may gave fixed
error, audio time signals always several seconds out.

PC with standard synchronisation, very poor. With Meinberg NNTP and
very short re-synch interval - pretty accurate.