OT accurate time checks?

[Harry Bloomfield]

Tim Watts used his keyboard to write :

I used to use one back in the 1980's, but a sync every thirty seconds is more than enough.

[The Natural Philosopher]

I am fairly sure that somwehere in all of this an ntp daemon 'works out' how much the real time clock is drifting between time server updates and adjusts the kernel clock periodically In Linux, anyway.

"ntpd uses the adjtime(2) system call to correct the local system time without causing time jumps. Adjustments of 32ms and greater are logged using syslog(3). The threshold value is chosen to avoid having local clock drift thrash the log files. Should ntpd be started with the -d or

-v option, all calls to adjtime(2) will be logged.

After the local clock is synchronized, ntpd adjusts the clock frequency using the adjfreq(2) system call to compensate for systematic drift."

(man ntpd)

Isnt it wonderful to have an operating system where all this is just DESIGNED IN from the word go..

[polygonum]

I was reading about doing exactly that last night. And pondering why the time on my GPS depends on me entering it manually?

[Clive George]

I remember building a clock from a kit which used the Rugby signal. Reception was never a problem though, since we lived about 5 miles from it :-)

[jgh]

No, it's the start of the last pip.

Each pip starts at the x.00 second point, at 55.00, 56.00, 57.00,

58.00, 59.00 and 00.00. The first five five are 0.1s long, the last is 0.5s long. The reference point is the start of each pip.

The pips are calibrated so that they are UTC accurate 160km from the London transmitter so averaging out the light-speed lag across thr country.

JGH

[Grimly Curmudgeon]

Mine probably is too. Once I installed W7 and let its own time checker get on with it, I no longer needed to be arsed with the various time checkers I'd used over the years - some of them quite good though. The best was Dimension 7, which also acted as a timekeeper for other PCs on my network.

[Mike Tomlinson]

En el artículo , Clive George escribió:

I got one off Ebay a couple of years ago. it works, but is sensitive to RFI interference - if I put it next to the TV for instance, it loses the time signal.

The 'Rugby' signal is now transmitted from somewhere in Cumbria IIRC.

[John Williamson]

So the story we were told about the last pip being longer to account for the difference between UTC and local time when they changed it from the standard length was a load of rubbish?

The BBC get it wrong again...

That wouldn't surprise me.

[Percy]

On Tue, 21 Aug 2012, "John Williamson" writ:

OK, understood. I'm amazed at your reaction time!

OK, thanks for the explanation.

[Frank Erskine]

That's what I'd have thought, since the gap between pips seems to be the same. Were it the end of the 'long' pip, it would have to start sooner.

[PeterC]

2 seconds. Such tolerances are outside the design specification of the W32Time service.'

button and replace apps' buttons on the Task Bar with icons, show a clock, day, date and an undocumented feature is that adding MM to the clock's display shows RAM left as well.

[Brian Gaff]

I'd have though gps, though delayed was pretty accurate as otherwise its not going to work. The other digital platforms are very inaccurate. There are still time standard transmissions on short wave of course but any reception frequency depends on propogation at the time of day needed. Ther are supposed to be some frequency shifted mod signals on the Long Wave stations run by the bbc and some others. There is the time standards in the UK and Germany used by radio clocks as well, but these are on a very low frequency and I've not seen any direct display receivers about at affordable costs.

Brian

[Harry Bloomfield]

I cannot think why it would need that. The GPS data received each and every second, contains a full set of data for time and date. What GPS satnav's sometimes need is some help to work out where they are if they have been off for a while and their table of where the satellites should be has become out of date, or it has been moved a large distance to a new location whilst off - leave it to its own devices for a few minutes and it will manage to sort itself out anyway.

[Mike Lane]

Mike Tomlinson wrote on Aug 22, 2012:

Many wristwatches do that. Mine synchronises with the transmitter in Anthorn, Cumbria every 24 hours. If that fails it tries the one in Mainflingen, Germany.

[Mark]

Announcers will talk over absolutely anything nowadays.

[Mark]

The Windows Time service is a NTP client and can be configured to set the clock accurately.

[Mark]

Please explain how it does this.

[Harry Bloomfield]

PC's actually use two clocks. A battery backed CMOS RTC clock which maintains the time whilst the system is off. When the PC is turned on, the data is transferred into memory, where the PC itself then does the counting to maintain that separate from the hardware clock's time interrupt driven.

So there are two possibilities for drifting accuracy - the CMOS RTC's crystal and the CPU's crystal whilst the PC is on and running. A time sync adjustment has to correct both of these clocks.

I use this VB script to alter the time interval between my PC syncing itself via the time servers.

You just need to run it once (ever), to make permanent changes to the sync interval...

'xp_time_sync.vbs - Change the Internet Time Update Interval '© Doug Knox - revised - 5/10/2002 'This code may be freely distributed/modified 'Downloaded from

'Thanks to Gregory Phillips for catching an error when clicking Cancel.

Option Explicit On Error Resume Next

'Declare variables Dim WSHShell, p1, p2, cn, newtime, mycheck, ev, X, Y

'Set the Windows Script Host Shell and assign values to variables Set WSHShell = WScript.CreateObject("WScript.Shell")

p1 = "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config\UpdateInterval" p2 = "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient\SpecialPollInterval"

'This section writes the correct values to the Registry

ev = WSHShell.RegRead(p2) ev = ev / 3600

cn = ""

Do While IsNumeric(CN) = False

cn = InputBox("Enter the number of hours"& vbCR & "between Internet Time updates" & vbCR & vbCR & "The current Setting in hours is: " & ev & vbCR & vbCR & "The default value is 168 hours (7 days).","Value Entry","24")

If IsNumeric(cn) = False Then MsgBox "Please enter a number!",4096,"Error!" End If

If cn = "" Then Exit Do End If

Loop

If cn "" AND cn > 0 Then

X = InStr(cn,".") cn = Left(cn,X+2)

newtime = cn * 3600 WSHShell.RegWrite p1, newtime, "REG_DWORD" WSHShell.RegWrite p2, newtime, "REG_DWORD" MsgBox "The Internet Time update interval has been changed." & vbCR & "Reboot your computer for the change to take effect.",4096,"Finished"

Else

If cn = "" Then MsgBox "The Internet Time update interval has NOT been changed.",4096,"Cancelled" Elseif cn

[Harry Bloomfield]

From a small company by the name of something like Cambridge Kits?

[Harry Bloomfield]

Brian Gaff explained :

The radio clocks and watches receive the VLF time standards.