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Time.is

time.is

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Re: Time.is

#51

Post by dfc »

A lot of people are making disparaging comments about the acccuracy of the site's time estimation with little or no explanation/data. All things considered (three samples to estimate clock deltas and network delay) the time estimation is fairly accurate.

time.is reports my clock is:

  -0.004 seconds (±0.021 seconds).
I have a stratum one time source on the local network (gps+pps) and my ntptime agrees with the time.is estimation:

  dfc@bushido:~$ ntptime 
  ntp_gettime() returns code 0 (OK)
    time d3077752.4160a634  Sun, Mar 11 2012 15:11:14.255, (.255381196),
    maximum error 260579 us, estimated error 3294 us, TAI offset 34
  ntp_adjtime() returns code 0 (OK)
    modes 0x0 (),
    offset -4842.630 us, frequency 8.446 ppm, interval 1 s,
    maximum error 260579 us, estimated error 3294 us,
    status 0x6001 (PLL,NANO,MODE),
    time constant 10, precision 0.001 us, tolerance 500 ppm,
NB: this is my laptop. so powersaving, heat fluctuations are adding a decent amount of uncertainty from a metrological standpoint.

Re: Time.is

#52

Post by bbx »

icebraining wrote: post #24
bbx wrote: post #6

Exactly what I needed. For the last few weeks, I've been trying to increase my productivity by getting rid of time tracking. So I decided to hide my computer's clock. Sometimes, like when I have an appointment, I still need to check what time it is. Googling "time" doesn't always work (I don't know why exactly). So I bookmarked this site [1] but the information density is so high that I need to scan the page in order…

What OS do you use? I usually just type 'date' on the terminal.

Mainly Win 7. Otherwise Mac OS X. Sometimes Win XP, and very rarely Ubuntu.

But I almost never have a terminal open (and don't have a shortcut for that either) whereas Firefox almost always is. So I'm just 1 click away rather than 4 characters away.

You taught me something though (I highly prefer typing on a keyboard than using a mouse or, worse, a touchpad) and I wish I had to spend more time in a terminal.

Re: Time.is

#54

Post by apaprocki »

phillmv wrote: post #30
apaprocki wrote: post #21

Earlier quoted context omitted.

It means that they didn't apply the latest tzdata2012a or b update released the first week of March which contained the America/Santiago zone change.

Time is a surprisingly difficult subject to get right.

Governments are free to change timezone rules at will with no real advance notice. Case-in-point, tzdata2012b was just published a few days ago and already on the tz mailing list Morocco's DST date is changing and Haiti apparently changed as well.

The problem is exacerbated by the fact that most systems rely on OS tzdata instead of shipping it themselves, yet in many places the administration of the OS is separated / walled off from the devs who maintain the apps which actually suffer from the bugs.

I feel bad for users who live in countries whose governments play with DST law on a whim, because they are certainly destined to encounter bugs throughout the Internet because it isn't always reasonable to ask all administrators around the globe to patch all production systems in a matter of a few days.

Re: Time.is

#55

Post by phillmv »

dfc wrote: post #48
phillmv wrote: post #29

Earlier quoted context omitted.

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?

*inspects the page

Yeah, you're right. That's not so bad.

It just seemed like it was claiming a lot of precision that, from my own experience of javascript, browsers and network latency, seemed a bit over the top. (Granted, on the order of magnitude of seconds, I'll accept that. Less than 100 ms and I grow suspicious).

Re: Time.is

#56

Post by apaprocki »

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…

In order to achieve the highest possible accuracy, you have to bring in your own hardware. We use appliances with internal rubidium oscillator clocks which also synchronize with the signal from all visible GPS satellites. This is as good as one can get if you really want to ensure proper time without having an external dependence on a third party or network.

edit: A paper from 1989 on the subject: http://tycho.usno.navy.mil/ptti/1989/Vol%2021_14.pdf

Re: Time.is

#57

Post by dfc »

roryokane wrote: post #50

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…

UTC is a "paper clock." The calculation of UTC has nanosecond error, not multisecond error. The most recent data for the calculation of UTC:

ftp://ftp2.bipm.org/pub/tai/publication/cirt.290

Time is a really tricky and interesting topic. I would start with:

"From Sundials to Atomic Clocks: Understanding Time and Frequency"

http://www.nist.gov/timefreq/general/pdf/1796.pdf

"Originally published in 1977, this full-length book provides a comprehensive, easy-to-understand introduction to the field of time and frequency. Readers of nearly all ages and educational backgrounds should find it enjoyable. 306 pages."

Re: Time.is

#58

Post by phillmv »

roryokane wrote: post #50

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…

Well… it's an arbitrary standard. We just call a day one full rotation of the earth, and we just happen to divide it into 24hr periods with 60 subdivisions.

Theoretically, you could measure the rotation of the earth and call that a day, but I have no idea how you would measure that down to the millisecond.

As to "Real Time", I don't know about the specific legalities, but the standard goes as follows: everyone uses UTC http://en.wikipedia.org/wiki/Coordinated_Universal_Time which is based off the International Atomic Time http://en.wikipedia.org/wiki/International_Atomic_Time

I too would be interested in how they picked the beginning epoch, i.e. "this moment right here is midnight from which all other seconds shall be referenced against" but in the grand scheme of things it doesn't matter - the only thing that matters is the standard we agreed to measure against.

Re: Time.is

#59

Post by dfc »

phillmv wrote: post #55
dfc wrote: post #48

Earlier quoted context omitted.

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?

*inspects the page Yeah, you're right. That's not so bad. It just seemed like it was claiming a lot of precision that, from my own experience of javascript, browsers and network latency, seemed a bit over the top. (Granted, on the order of magnitude of seconds, I'll accept that. Less than 100 ms and I grow suspicious).

what does your machine say for "ntpq -p" and "ntptime"?

Re: Time.is

#60

Post by dfc »

justincormack wrote: post #45
morsch wrote: post #39

Earlier quoted context omitted.

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.

Your cell network or you do not have multicast ntp enabled?
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