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Time.is

time.is

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Re: Time.is

#41

Post by ComputerGuru »

dfc wrote: post #37
ComputerGuru wrote: post #31

Earlier quoted context omitted.

The answer to your question is GPS devices. They're supposed to take into account (most of) what you mentioned, and even though consumer GPS devices are fairly cheap and not up to industrial or even military GPS, time is one thing they do right. In fact, for several projects that needed a reliable time source instead of using the (as you noticed) poorly implemented atomic clock radio frequencies, we would just buy GP…

NTP does a lot more than what you theorized about and none of it is trivial. FYI: Ping is a remarkably bad tool to gauge the accuracy of remote time source. What is the delay value from "ntpq -p" I highly doubt that Apple's time servers are your best bet for time synch. Use the pool.ntp.org servers, preferabbly with your country code: e.g. us.pool.ntp.org, ca.pool.ntp.org.

I removed the bit about NTP as it was mostly half-baked ramblings. I obviously didn't mean "ping" the tool, rather the process of "pinging" a remote address and gauging the response time, at the most basic.

My ntpq -p output:

        remote           refid      st t when poll reach   delay   offset  jitter
   ==============================================================================
    time.apple.com  .INIT.          16 u    -  512    0    0.000    0.000   0.000

Re: Time.is

#42

Post by dfc »

ComputerGuru wrote: post #41
dfc wrote: post #37

Earlier quoted context omitted.

NTP does a lot more than what you theorized about and none of it is trivial. FYI: Ping is a remarkably bad tool to gauge the accuracy of remote time source. What is the delay value from "ntpq -p" I highly doubt that Apple's time servers are your best bet for time synch. Use the pool.ntp.org servers, preferabbly with your country code: e.g. us.pool.ntp.org, ca.pool.ntp.org.

I removed the bit about NTP as it was mostly half-baked ramblings. I obviously didn't mean "ping" the tool, rather the process of "pinging" a remote address and gauging the response time, at the most basic. My ntpq -p output: remote refid st t when poll reach delay offset jitter ============================================================================== time.apple.com .INIT. 16 u - 512 0 0.000 0.000 0.000

Your computer has not successfully contacted the time.apple.com server. If it had the refid would not be INIT and your "reach" value would not be 0.

what happens if you change your time server to us.pool.ntp.org? (Substitute your country code for "us".)

Preferably you should have more than one server. The ntp reference implementation on osx is a little goofy because of the GUI configuration. But I think if you put us.pool.ntp.org,us.pool.ntp.org,us.pool.ntp.org for the server your computer will try to spin up three ntp connections. Atleast three, never two...

"A man with one watch knows what time it is; a man with two watches is never quite sure."

Re: Time.is

#43

Post by ken »

mwexler wrote: post #14

I like Time.gov, personally; it was the first site I ever found around this concept and so it has a soft spot. I keep finding all my physical atomic clock synced clocks (yes, I have more than one, they are cheap these days) disagreeing, sometimes by 2 seconds or more, which makes me laugh (great ideas ruined by poor implementation). I find many of the web sites (listed in comments or the original post) to also differ…

When I was a kid, my dad would always set our clocks by tuning the radio to one of the atomic clock broadcasts from Fort Collins. This might be the same source as your automatically synchronized clocks, but the advantage is that it's human-listenable, and not going through any computer networks or algorithms between Colorado and you.

https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time...

Re: Time.is

#44

Post by dfc »

mdda wrote: post #33

For those alarmed at the offset... # yum install ntpdate # ntpdate -u ntp-1.vt.edu # hwclock -w "Your time is exact!"

ntpdate is dead and is discontinued. Use an actual daemon to govern your time source.

I thought redhat installed ntpd or chrony by default. I know chrony is the default for the next fedora release. If you have ntpd/chronyd installed your advice is horrible and not just because you pointed everyone to Virginia Tech's time server.

Re: Time.is

#45

Post by justincormack »

morsch wrote: post #39
mdda wrote: post #33

For those alarmed at the offset... # yum install ntpdate # ntpdate -u ntp-1.vt.edu # hwclock -w "Your time is exact!"

This is an unobtrusive app that does the job for Android (root required/recommended): https://play.google.com/store/apps/details?id=ru.org.amip.Cl... My ZTE Blade/CM7 was obnoxiously bad at keeping time, probably a software bug or something.

Not sure why Android does not have ntp built in. My network does not broadcast a time signal, maybe it is just assumed they all do.

Re: Time.is

#46

Post by dfc »

ken wrote: post #43
mwexler wrote: post #14

I like Time.gov, personally; it was the first site I ever found around this concept and so it has a soft spot. I keep finding all my physical atomic clock synced clocks (yes, I have more than one, they are cheap these days) disagreeing, sometimes by 2 seconds or more, which makes me laugh (great ideas ruined by poor implementation). I find many of the web sites (listed in comments or the original post) to also differ…

When I was a kid, my dad would always set our clocks by tuning the radio to one of the atomic clock broadcasts from Fort Collins. This might be the same source as your automatically synchronized clocks, but the advantage is that it's human-listenable, and not going through any computer networks or algorithms between Colorado and you. https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time...

"The advantage is that it's human-listenable, and not going through any computer networks or algorithms between Colorado and you." That is an advantage?

The Fort Collins signal is awful in the northeast. If you want to deal with the disadvantages of not using advanced computer algorithms to govern your clock i would recommend the USNO's phone service:

Time Voice Announcer, Washington, DC: 202-762-1401 & 202-762-1069 (DSN 762-1401, 762-1069)

Time Voice Announcer, Colorado Springs, CO: 719-567-6742 (DSN 560-6742)

Re: Time.is

#47

Post by dfc »

guylhem wrote: post #34

I like it a lot. Easy to remember URL. However the services offered are not so good. At least there is no RFC 867 and RFC 868 date on port 37 and port 13. This is deprecated, I know, but rdate is still the easiest way to fix the date on a system which do not require precision. I did run my own minimal daemon on my DSL modem for the various gizmos I have that include busybox (thus rdate) and where recompiling to get a…

rdate is awful that is why NIST killed it. If you want a fire and forget time check:

  sntp pool.ntp.org

Re: Time.is

#48

Post by dfc »

phillmv wrote: post #29
mwexler wrote: post #14

I like Time.gov, personally; it was the first site I ever found around this concept and so it has a soft spot. I keep finding all my physical atomic clock synced clocks (yes, I have more than one, they are cheap these days) disagreeing, sometimes by 2 seconds or more, which makes me laugh (great ideas ruined by poor implementation). I find many of the web sites (listed in comments or the original post) to also differ…

MY understanding of the issue confirms that you would basically need a js implementation of ntp in order for any of this to work. That's why I laughed when Time.is tried to tell me that my clock was off by 1.8 seconds. Barring the sentence above, it just has no way of determining that.

All things considered it is not such a bad estimate of the time. It looks like it makes it queries the local clock three times to get an estimation of the clock deltas and network delay . Why do you think 1.8 seconds is wrong? What is your ntpq billboard?

Re: Time.is

#50

Post by roryokane »

I'm wondering how atomic clocks in general get set in the first place. Did, at some point, scientists calculate when the sun was exactly overhead Greenwich and call that noon? Because I would think that that calculation would have a multi-second error, so setting your clock to the second would be pointless.

Or maybe there is no such thing as "actual physical time" and there is only what people have agreed to call the standard. But in that case why do time sources, such as time.gov and time.windows.com, still give different times? I would think Microsoft would have fixed any bugs in their NTP implementation by now, so it's not that. If it's just politics about nobody wanting to move to someone else's time, then there's no way to tell which source is the real standard, so your most practical choice is to synchronize your clock to the times you deal with. That is, set your clock to your clock at work, or an average of your friends clocks, or whatever source they get their time from. I don't mind the existence of central time sources, because they are better than having to go out and find someone else's clock, but they shouldn't call themselves official if they aren't actually official.

So, does anybody know how the starting time for central time sources is chosen, and if any source is worthy of being called "the real time"?

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