Most accurate device time?

goodValue

I have three digital devices whose clocks differ by a few seconds.
Is there any way of finding out which is the most accurate on any particular day?
This would need to work in the UK and EU, so couldn't use the BBC pips.

MeadowsVale

I have a radio controlled wall clock I bought from Amazon last year. Sets itself and the time is bang on.

unforeseen

MeadowsVale said:

I have a radio controlled wall clock I bought from Amazon last year. Sets itself and the time is bang on.

You would need one that will synchronise with the European time standard signal as well (based in Germany, I believe).
The UK time standard broadcast from Anthorn doesn't reach the continent very well. My watch can never sync when in Spain

wongataa

A handheld GPS receiver will show the correct time (as long as it displays the time) when it is locked on.

Neil_Jones

goodValue said:

I have three digital devices whose clocks differ by a few seconds.
Is there any way of finding out which is the most accurate on any particular day?
This would need to work in the UK and EU, so couldn't use the BBC pips.

If these are radio controlled devices then a lot depends on when they last responded to the time signal.  Given enough time even all radio controlled clocks will eventually drift if they can't see a signal (environment, outage, maintenance, etc) but for the most part we're probably only talking about a couple of seconds per day on the drift, but most devices will try to re-sync daily.

The one in Germany (DCF77 which is in Frankfurt) tends to be the default for European clocks and those that come from the likes of Lidl and Aldi (for obvious reasons) and has a wider distance - somewhere around 1200 miles rather than the 900 odd mile that NPL has.  France has a more powerful transmitter which is good for over 2000 miles radius, but apparently requires a more complex receiver in the clock. 

unforeseen

TBH I would question the 900 mile range of the NPL one. It has never been the same since Qinetic took over after the BBC shut down their aerial farm at Rugby. 
I don't think sitting at sea level with the Pennines & the lake district mountains shielding it from the south & southeast of half the country does a lot for the transmission coverage.
I know it's LF and tends to 'ground hug' but those mountains cause a hell of a shadow. Troposcatter won't cover the 'hole' at such short distances

Eyeful

You can play around with this.
 Use the search bar at top of page to find time somewhere else (example New York).
https://time.is/

goodValue

 but most devices will try to re-sync daily.

Does the Android Clock app re-sync at the same time-of-day, each day, or will this be dependent on the phone make/model?

Eyeful

1. As I understand it:
The Android clock does not have a set routine every day for checking the right time—it could be any time, depending on the phone.
Different phones and companies may do it their own way, so not all Android phones check the time at the same moment.

2. Why do you need such great time accuracy any way?

Neil_Jones

unforeseen said:

TBH I would question the 900 mile range of the NPL one. It has never been the same since Qinetic took over after the BBC shut down their aerial farm at Rugby. 
I don't think sitting at sea level with the Pennines & the lake district mountains shielding it from the south & southeast of half the country does a lot for the transmission coverage.
I know it's LF and tends to 'ground hug' but those mountains cause a hell of a shadow. Troposcatter won't cover the 'hole' at such short distances

NPL used to claim over 900 miles, though whether I've misremembered that from the Rugby days I don't know.

goodValue said:

 but most devices will try to re-sync daily.

Does the Android Clock app re-sync at the same time-of-day, each day, or will this be dependent on the phone make/model?

In my experience as soon as you manually change the clock on an Android phone and then tell it to get its time and date from the network it updates straight away.  This is irrelevant on phone make/model so I can only presume its being sent by the networks.

Android documentation on this is here:

https://source.android.com/docs/core/connect/time/network-time-detection - "Android's default network time sync uses SNTP with a single time query approximately once a day to try to ensure it always has a recent time signal."

goodValue

In my experience as soon as you manually change the clock on an Android phone and then tell it to get its time and date from the network it updates straight away.

I didn't realise I was opening a can of worms.

The technical details in the link were too much for me, but I did come away with the following thoughts:

There are two sources of error, latency and drift.

It sounds like the likely latency error would be much less than the  maximum theoretical error of 2.5 seconds.

So for devices more than, say, a second in error, drift will be the major souce of error.

So, by deselecting network time, and then selecting it, the sync signal will be received, and the phone will likely be accurate to within a second.

Does this sound reasonable?