[Nottingham] "ntpq -p" displayed flags

Martin martin at ml1.co.uk
Fri Jan 27 01:22:46 UTC 2012

On 26/01/12 16:03, Camilo Mesias wrote:
> Hi,
> On Thu, Jan 26, 2012 at 2:26 PM, Martin <martin at ml1.co.uk> wrote:
>> What I have run out of time with is... How do you know what accuracy you
>> are running with? What timing error can be expected from what ntpq can
>> tell you? (Simply :-) )
> That's a good summary on your webpage - would have been helpful if I'd
> found something like that instead of the lore-filled manuals I managed
> with.
> Accuracy wise, it should be low ms, provided it's synced. In practical
> terms, say if you have a roomful of equipment all flashing LEDs in
> some pattern, they will be synchronised and appear to all be flashing
> together.

Yes... But what numbers to you use from the ntp output to assess the
accuracy achieved? And can they be believed? ;-)

> It's really showing its age now that every cellphone and gadget can
> have GPS and accurate time for a very low cost.

Yep... What we need is a little further advice from our group's GNSS
expert. There's various sub-£20 GPS dongles available but the web
recommended devices for use as a time source are still nearer to £100 :-(

After doing the write-up, I'm rather tempted to play further... More a
question of (available, spare,) time!

> Will you be writing up PTP (IEEE 1588) next? ;-)


In any case, there are various other peering systems appearing that are
fully distributed that the MPAA and RIAA cannot so easily vandalise.

So, my latest version of a helpful page for ntpq stands at:

“ntpq -p” output

There's a couple of questions at the end there for some of the detail...

And have I found a discrepancy for how the poll times are displayed?


Martin Lomas
martin at ml1.co.uk

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