Time Standards

updated 2002-11-23.

Related pages:

online time servers

Date and Time Standards

The International Standard for the representation of dates and times (ISO 8601:1988) http://www.cl.cam.ac.uk/~mgk25/iso-time.html /* was http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html */ mentions a few different notations.

Here is the one chosen by W3C for the standard HTML 4.0 Web notation.

Copied from http://www.w3.org/TR/REC-html40/types.html#h-6.11 (also mentioned at http://www.w3.org/2001/06tips/iso-date ) :

The format is:



     YYYY = four-digit year
     MM   = two-digit month (01=January, etc.)
     DD   = two-digit day of month (01 through 31)
     hh   = two digits of hour (00 through 23) (am/pm NOT allowed)
     mm   = two digits of minute (00 through 59)
     ss   = two digits of second (00 through 59)
     TZD  = time zone designator

The time zone designator is one of:

indicates UTC (Coordinated Universal Time). The "Z" must be upper case.
indicates that the time is a local time which is hh hours and mm minutes ahead of UTC.
indicates that the time is a local time which is hh hours and mm minutes behind UTC.

Exactly the components shown here must be present, with exactly this punctuation. Note that the "T" appears literally in the string (it must be upper case), to indicate the beginning of the time element, as specified in ISO 8601

If a generating application does not know the time to the second, it may use the value "00" for the seconds (and minutes and hours if necessary).

End copy.

Chris Garrod http://sioviz.ucsd.edu/~garrod/y10k/ proposes yet another time and date notation:

"Let's simply treat all dates as numbers. ... 19990102.103444 translates to: Sat Jan 2 10:34:44 PST 1999. ... Simply stated, my solution provides fixed sizes for the month, day, hour, minute and second. Room is available to extend the year indefinitely, and to provide as much additional precision to the seconds as required by any application. The above format can be used in a variety of ways: omit the time entirely, and it still sorts properly, omit seconds or minutes when unknown or they don't matter. In all forms, time as stated is a monotonically increasing number, where the fully qualified date is an integer, and the time is it's fractional part stated in .hhmmssnnnnnnnn format."

exact time

measuring time (almost) exactly.

Exact Time

(for more global standards, see
The SI prefixes, the metric system, and related info.)

From:  (Jim Carr)
Newsgroups: sci.physics.relativity
Subject: Re: The Absurdity of SRT
Date: 28 Feb 1997 22:38:28 GMT
Organization: Supercomputer Computations Research Institute
Lines: 48

 (Ken H. Seto) writes:
>But how do you know how many cycles is one second if you don't use the
>earth value to set the clock?

 You go to the NIST web site, follow the FAQ, and read the number.


] How is the second defined?
] The international definition of a second is "the duration of 9 192 631 770
] periods of the radiation corresponding to the transition between the two
] hyperfine levels of the ground state of the cesium atom."

 Hmmm.  Did I type that wrong in an earlier post?

>That's why Einstein used the speed of
>light to set the clocks in the other frames to cause the speed of
>light to have the same value as that of the earth--this is what is
>known as E-Syn.

 I don't know where you get this misconception.  E-synch concerns
 how one synchronizes a set of clocks that are at different places
 but all at rest in a *single* reference frame.  Some Gedanken
 experiments use an event such as the emission of a light pulse to
 define a point in spacetime for two different inertial frames,
 but this has nothing to do with the length of a second.

 In principle, each frame has a Cs clock, like


 and uses it and a fast counter to define its second.

>Only if you say that a seocnd in the other frame is represent by a
>diffenert number of cycles of the cesium atom and that number of
>cycles of the cesium atom is, in turn, set by the speed of light on

 I think this represents a confusion between what is done in each
 frame and how that experiment looks to an observer in another frame.

 James A. Carr        |  "Whatever."
    http://www.scri.fsu.edu/~jac/       |
 Supercomputer Computations Res. Inst.  |      George Herbert Walker Bush
 Florida State, Tallahassee FL 32306    |

clocks by John Harrison

John Harrison solved the Longitude Problem

Daylight Saving Time (DST)

and alternative schemes: metric time, etc.

Daylight Saving Time http://webexhibits.org/daylightsaving/b.html ``The official spelling is Daylight Saving Time, not Daylight SavingS Time.''

One of the members of the "metric time" web ring. http://members.tripod.com/~zoam/metrictime.html

Some URLs About Time http://yorty.sonoma.edu/courses/a231/time_urls.html "technical dicussion of time standards on the Internet," "Daylight Nuisance Time", "The 25 Hour Day", and other useful and not-so-useful links.

End DST http://www.standardtime.com/ arguments against DST (also has clocks displaying the current time of all 4 U.S. time zones), and switching to only 2 U.S. time zones.

non-Y2K software problems

Here are some errors resulting from software errors very similar to expected Y2K errors.

Y2K: the "Year 2000 Crisis"

I use ISO 8601 standard date notation , to avoid the "Y2K Crisis" around 1999-09-09 ( several months before 2000-01-01, the date most people think it will happen).

XDay notation is another way to avoid the problem http://www.bobbemer.com/XDAY.HTM (counts days from 763 Sep __) .

Information about Y2K:

Some online calendar resources:

Precision Timing Hardware

Surely there are lots of other equipment manufacturers out there. I'll try to add them to this list as you tell me about them.

wrist watches

DAV isn't currently interested in wristwatches-as-jewelry. DAV is interested in wristwatches and pocket watches since they lay at the intersection of several things I'm interested in:

  1. user_interface.html good user interfaces. More thought has been put into making wristwatches comfortable and quick-to-read than any other electronic device I know (although much of this thought occured *before* electronics really existed ... and many interesting user-interface ideas were implemented in early mechanical wristwatches and pocket watches).
  2. wearable_electronic.html wearable electronics (which deals with compromises and synergism between comfort, weight, low-power design, usability, etc.)
  3. VLSI electronic circuit design vlsi.html (unfortunately, it's far more difficult to find information about the internals of electronic watches than mechanical watches, perhaps because one can just take a mechanical watch apart and *see* how it works, while nearly all the interesting stuff about an electronic watch is hidden under a black blob of goo. The simplest way to get this information is through the company that made it -- and too often we have the catch-22 Sorry, that information is too new -- it's a trade secret Sorry, that information is too old -- it's useless to our competitors now, but it's useless to us as well, so we shredded it. )
  4. 3d_design.html the process of intelligent design, and the moving limits of ``what is possible with current technology''. The idea that one can take a design and improve on it ... Early horologists put a lot of effort into improving the accuracy of the clock they were working on (compared to their ``competitors'' and to previous clocks they built), and so they were on the cutting of technology. Once we got to quartz-crystal accuracy, wristwatch accuracy has reached a plateau -- since humans can't tell the difference between a (hypothetical) perfectly accurate wristwatch vs. one that's off by a few hundredths of a second, there's no point in improving the accuracy of the wristwatch. So wristwatch improvements have gone to *other* areas (time between rewinding/replacing batteries, comfort, legibility, etc.), and there's not as strong a motivation for improved time accuracy (although people at NIST and elsewhere are still pushing the envelope of time and frequency precision, because some applications *need* more precision -- pushing improved design in 2 directions: improving accuracy (to make possible applications like GPS that require higher precision than a wristwatch) and reducing cost .

    There's also the ``blindness'' of humans in not recognizing when something really is a practical improvement. Fashion is fine when it doesn't interfere with practicality. When one way is objectively better than another, let's use the better way.

    There's also the blindness of humans in deciding not to pursue a technology (or designing crippled products based on that technology) that could reduce sales of some other product(s) in the company (the Swiss and quartz watches, IBM and the PCjr, ...). Think, man: if *you* don't sell this, then what happens when *other* companies sell this ? (Looks like I'm not the only one that feels this way: see "Economics of electronic Research and Development" http://airborn.com.au/spec/econ.html )

General wrist watch information:

specific watches and companies

see also machine_vision.html#GPS_wristwatches and Wrist Camera Watches machine_vision.html#wrist_cameras and wrist computers wearable_electronic.html#wrist


see also #GeoClock Things to consider for my sundial:

more sundial information:



time synchronization software for your computer


Notes on WWV http://www.SCIAM.COM/1998/0498issue/0498wonders.html

Current time in cities all over the world http://www.lucent.com/what/international/

The Royal Greenwich Observatory would appear to be the authority on gnomonics http://www.ast.cam.ac.uk/RGO/leaflets/sundials/sundials.html , the study of sundials.

Clocks and Time http://www.ubr.com/clocks/


CST (+06:00)
Central Daylight Saving (+05:00).

Started 1998-01-08

Send comments, suggestions, syntax errors http://validator.w3.org/check?uri=http://rdrop.com/~cary/html/time.html , bug reports to
David Cary

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