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, perhaps for similar reasons of implementation choices.
I would presume all the sites work off various implementations of NTP, http://www.ntp.org/ plus some trusted source.
I guess my question is: has anyone found a site which is really, really accurate by reducing all the latency and lag, so what you see on the screen really is, to whatever precision, accurate? And would said person have access to a really good source for the comparison point? I don't seem to have one. Yes, I should have stopped at 3 so that I could pick the 2 closest ones (like the old saying: 1 clock is unsure, 2 clocks are worse, but 3 at least lets you make a decision)
I wonder, would you need to have NTP on the client side synced to a trusted source (say, in java, flash, or javascript) to get a good reading? Any server serving over HTTP induces lag, I would think, and NTP is supposed to account for transmission delays, or so I recall.
Thanks for sharing, another interesting time site to add to the collection.
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 GPS chips to just extract the time signal.
<removed NTP stuff>
I simply don't have any clocks that aren't part of electronic devices, my wristwatch being the exception (but it's analog (Roman numerals, even :P) and only has second accuracy anyway, so I don't fuss about it).
Simply put, all my devices take care of all this for me. My MacBook and Windows 7 work desktop are both configured to sync to the Apple NTP servers (lowest ping for me, AND they're always up. Microsoft's are down a good 10% of the time in my experience). My cell phone gets its signal from God knows where (iPhone 4S - it could technically be using one of 4 different sources) but is always more or less in sync with the rest (I just checked with time.is for what little that is worth, however, and while my MacBook says that my time is within the margin of error "The difference from Time.is was -0.007 seconds (±0.018 seconds).", my iPhone returns "Your clock is 0.5 seconds slow" - but I would trust my iPhone's NTP implementation over time.is' response as its the same OS X NTP that got it "right" on my MacBook) as it can theoretically use a) GPS b) GSM/CDMA towers c) NTP d) time from PC sync.
All my other electronic devices fall in the same category. Garmin nüvi (GPS), Kindle (NTP, auto configured), Cisco IP Phone (NTP, manually configured), Brother printer (NTP, manually configured). I purposely do not set my microwave clock because a) I'll never get it right, and b) any time the power cuts, it resets and in 2012 they're still too stupid to add a 5 cent battery to keep the time in case of power outage.
Radio controlled clocks are subject to numerous sources of error. However two seconds is pretty bad, according to NIST the RCC "should always be accurate to within one second of UTC, assuming that they synchronize at least every other day and that their quartz oscillator is of reasonable quality." How far do you live from Fort Collins, CO? I have included some WWVB references at the end...
My GPS + Pulse Per Second fed ntp server is remarkably better than a radio controlled clock. The Sure GPS evaluation board probably costs less than your radio controlled clock:)
dfc@ronin:~$ ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
oGPS_NMEA(0) .GPS. 0 l 12 16 377 0.000 0.001 0.001
bonehed.lcs.mit .CDMA. 1 u 32 64 377 51.365 0.670 0.364
rooster.stonybr .CDMA. 1 u 14 64 377 49.019 6.141 0.445
navobs1.oar.net .USNO. 1 u 1 64 377 57.310 9.494 0.456
meg.ee.lbl.gov .PPS. 1 u 1 64 377 88.639 -2.204 0.270
dfc@ronin:~$ ntptime
ntp_gettime() returns code 0 (OK)
time d3076554.79d48450 Sun, Mar 11 2012 13:54:28.475, (.475899416),
maximum error 234 us, estimated error 0 us, TAI offset 34
ntp_adjtime() returns code 0 (OK)
modes 0x0 (),
offset 0.856 us, frequency -32.941 ppm, interval 1 s,
maximum error 234 us, estimated error 0 us,
status 0x2001 (PLL,NANO),
time constant 4, precision 0.001 us, tolerance 500 ppm,
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.
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.
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.
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.
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"?
"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."
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.
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.
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 to get the time.
Time.is works quite well, with useful customization options, though it still carries bits of useless information (like the time zones at the bottom). But the time's font size is big enough to trigger instant focus.
UPDATE: as guptaneil pointed out, clicking the time (or navigating to http://time.is/just) removes all the clutter. Thanks for the tip.
Nice job on this. I usually use http://everytimezone.com but I like how I can configure this with the zones that matter to me. It would be nice if I could easily use my favorites when doing the Here -> There comparison.
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 ntp would be overkill. (the right day and the right hour are more than enough)
time.nist.gov removed RFC 867 (port 13) and 868 (port 27) support. time-nw.nist.gov kept it a bit longer, then I used by DSL modem, which went in RMA and so guylhem.org is also down.
I'll try to email the author and offer to give a hand.
The handling of internationalization is surprisingly good. Texts, including town names, are almost all shown in the preferred language, and the size variations introduced by the translations are well handled.
I would still prefer to have the option to select the timezone. Sometimes I want to attend some workshops that announce the time in one of the US timezones and its always difficult to do the conversion.
I imagine that the author of the page has some scientific background and therefore feels that it is appropriate to publish the margin of error alongside any estimation.
Simple, but awesome. About two years ago I had the idea (but never implemented) to try and re-make various since use web tools and calculators using modern web technology. Things like interest/mortgage calculators, voltage drop calculators, difference between two dates, etc.
So many of them like Time.gov rely on stuff like Flash or Java, or 1998 style Javascript, which I don't really dig. Definitely a nice little hole there for making something cool.
The clock display is nice but not a killer for me. Here&There time comparison in different time zones is the best I have seen. Full page calendar with multiple months is very simple but works great for me.
This is becomes my favorite site for time/date related stuff.
My little Ubuntu machine is -0.018 seconds (±0.009 seconds).
My MBP is -0.012 seconds (±0.021 seconds).
I recommend you add a percentile score of exactness, along with breakdowns based on platform, and suggestions about what to do if the percentile is disappointing.
I am seeing roughly +/- 0.1s accuracy range on my browser. Can someone please enlighten me on why we cannot reduce this further? I assume this page has <100ms response time, can't they get to a better accuracy range?
[+] [-] mwexler|14 years ago|reply
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, perhaps for similar reasons of implementation choices.
I would presume all the sites work off various implementations of NTP, http://www.ntp.org/ plus some trusted source.
I guess my question is: has anyone found a site which is really, really accurate by reducing all the latency and lag, so what you see on the screen really is, to whatever precision, accurate? And would said person have access to a really good source for the comparison point? I don't seem to have one. Yes, I should have stopped at 3 so that I could pick the 2 closest ones (like the old saying: 1 clock is unsure, 2 clocks are worse, but 3 at least lets you make a decision)
I wonder, would you need to have NTP on the client side synced to a trusted source (say, in java, flash, or javascript) to get a good reading? Any server serving over HTTP induces lag, I would think, and NTP is supposed to account for transmission delays, or so I recall.
Thanks for sharing, another interesting time site to add to the collection.
[+] [-] ComputerGuru|14 years ago|reply
<removed NTP stuff>
I simply don't have any clocks that aren't part of electronic devices, my wristwatch being the exception (but it's analog (Roman numerals, even :P) and only has second accuracy anyway, so I don't fuss about it).
Simply put, all my devices take care of all this for me. My MacBook and Windows 7 work desktop are both configured to sync to the Apple NTP servers (lowest ping for me, AND they're always up. Microsoft's are down a good 10% of the time in my experience). My cell phone gets its signal from God knows where (iPhone 4S - it could technically be using one of 4 different sources) but is always more or less in sync with the rest (I just checked with time.is for what little that is worth, however, and while my MacBook says that my time is within the margin of error "The difference from Time.is was -0.007 seconds (±0.018 seconds).", my iPhone returns "Your clock is 0.5 seconds slow" - but I would trust my iPhone's NTP implementation over time.is' response as its the same OS X NTP that got it "right" on my MacBook) as it can theoretically use a) GPS b) GSM/CDMA towers c) NTP d) time from PC sync.
All my other electronic devices fall in the same category. Garmin nüvi (GPS), Kindle (NTP, auto configured), Cisco IP Phone (NTP, manually configured), Brother printer (NTP, manually configured). I purposely do not set my microwave clock because a) I'll never get it right, and b) any time the power cuts, it resets and in 2012 they're still too stupid to add a 5 cent battery to keep the time in case of power outage.
[+] [-] dfc|14 years ago|reply
My GPS + Pulse Per Second fed ntp server is remarkably better than a radio controlled clock. The Sure GPS evaluation board probably costs less than your radio controlled clock:)
Radio clock reference material:NIST Page on Radio clocks: http://www.nist.gov/pml/div688/grp40/radioclocks.cfm
"How accurate is a radio controlled clock" http://tf.nist.gov/general/pdf/2429.pdf
"WWVB Radio Controlled Clocks: Recommended Practices for Manufacturers and Consumers": http://tf.nist.gov/timefreq/general/pdf/2422.pdf.
[+] [-] ken|14 years ago|reply
https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time...
[+] [-] apaprocki|14 years ago|reply
edit: A paper from 1989 on the subject: http://tycho.usno.navy.mil/ptti/1989/Vol%2021_14.pdf
[+] [-] phillmv|14 years ago|reply
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.
[+] [-] antidaily|14 years ago|reply
[+] [-] dfc|14 years ago|reply
time.is reports my clock is:
I have a stratum one time source on the local network (gps+pps) and my ntptime agrees with the time.is estimation: NB: this is my laptop. so powersaving, heat fluctuations are adding a decent amount of uncertainty from a metrological standpoint.[+] [-] roryokane|14 years ago|reply
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"?
[+] [-] dfc|14 years ago|reply
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."
[+] [-] phillmv|14 years ago|reply
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.
[+] [-] troels|14 years ago|reply
[+] [-] bbx|14 years ago|reply
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 to get the time.
Time.is works quite well, with useful customization options, though it still carries bits of useless information (like the time zones at the bottom). But the time's font size is big enough to trigger instant focus.
UPDATE: as guptaneil pointed out, clicking the time (or navigating to http://time.is/just) removes all the clutter. Thanks for the tip.
[1] http://www.timeanddate.com/worldclock/city.html?n=328
[+] [-] guptaneil|14 years ago|reply
[+] [-] icebraining|14 years ago|reply
[+] [-] ElliotH|14 years ago|reply
[+] [-] mtr|14 years ago|reply
[+] [-] apaprocki|14 years ago|reply
[+] [-] time_is|14 years ago|reply
[+] [-] aeden|14 years ago|reply
[+] [-] libria|14 years ago|reply
[+] [-] Aramgutang|14 years ago|reply
Unlike English, which also has exceptions for "2nd" and "3rd", Armenian only uses a different suffix for "1st".
[+] [-] sushimako|14 years ago|reply
[+] [-] mrud|14 years ago|reply
[+] [-] djsla|14 years ago|reply
disclosure: worldtimebuddy founder.
[+] [-] guylhem|14 years ago|reply
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 ntp would be overkill. (the right day and the right hour are more than enough)
time.nist.gov removed RFC 867 (port 13) and 868 (port 27) support. time-nw.nist.gov kept it a bit longer, then I used by DSL modem, which went in RMA and so guylhem.org is also down.
I'll try to email the author and offer to give a hand.
[+] [-] dfc|14 years ago|reply
[+] [-] riobard|14 years ago|reply
[+] [-] moe|14 years ago|reply
It is labeled "DCF signal - precision time", yet is off by hours most of the time (jumps randomly).
I keep it for the entertainment value. Guests always have a good chuckle when they enter the bathroom at 16:41 and leave it at 23:41.
[+] [-] hrktb|14 years ago|reply
[+] [-] zarroba|14 years ago|reply
[+] [-] napoleoncomplex|14 years ago|reply
The add-on would be simpler, as a text-select and right click could show the selected time in your own time zone in the right-click menu.
It's something I've missed every single time some press conference or event is announced, and it just says 12:00 EST.
[+] [-] darklajid|14 years ago|reply
[+] [-] gwern|14 years ago|reply
[+] [-] dfc|14 years ago|reply
[+] [-] 7952|14 years ago|reply
[+] [-] tibbon|14 years ago|reply
So many of them like Time.gov rely on stuff like Flash or Java, or 1998 style Javascript, which I don't really dig. Definitely a nice little hole there for making something cool.
[+] [-] acerimmer|14 years ago|reply
[+] [-] ideaoverload|14 years ago|reply
[+] [-] cynwoody|14 years ago|reply
My little Ubuntu machine is -0.018 seconds (±0.009 seconds).
My MBP is -0.012 seconds (±0.021 seconds).
I recommend you add a percentile score of exactness, along with breakdowns based on platform, and suggestions about what to do if the percentile is disappointing.
[+] [-] iag|14 years ago|reply