updated 2002-11-23.
Related pages:
Is there another sunclock here ? http://www.thinktheearth.net/
In some ways related to #sundials .
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-MM-DDThh:mm:ssTZD
where:
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:
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."
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.
http://www.bldrdoc.gov/timefreq/faq/q26.htm
] 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
http://www.bldrdoc.gov/timefreq/museum/nist-7.jpg
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
>earth
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 |
John Harrison solved the Longitude Problem
a revolutionary turret clock for the stables at Brocklesby Park ... revolutionary because it required no lubrication. 18th century clock oils were uniformly poor and one of the major causes of failure in clocks of the period. Rather than concentrating on improvements to the oil, Harrison designed a clock which didn't need it. It was radical thinking of this sort that would be important later on, when he tackled the problem of designing a marine timekeeper.
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.
Here are some errors resulting from software errors very similar to expected Y2K errors.
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:
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.
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:
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.)
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:
-- http://forums.zdnet.com/group/zd.Speakeasy/cnet/cnetnt.tpt/@thread@135607@F@1@D-,D@ALL/@article@mark@135607?ROS=1&OC=75From J Vega
I've always been wildy "crazy" about the EXACT time. I'd love to have almost perfect accuracy in an affordable clock next to my bed. I try to keep my PC accurate to less than a tenth of a second. Old mental thing, I picked it up in the past, when I used to carry 4 different watches. The taxpaypers paid a fair bit of change for two of them, which I replaced every time I blew my nose until I was satisfied, at a cost of hundreds of dollars to the taxpayers every time I did. 1 second=700 feet, roughly. ...
From Rosalie Byrd
As a taxpayer I demand an explanation, J.
When did you 'used to carry 4 different watches' and why? And why were they so expensive? And why did I have to pay for them? ;-) ...
From J Vega
You got it, Rosalie...
When you drop explosive devices from an aircraft, just as important as where it lands is when it lands. It was common for Navigator/Bombadiers to go thru many watches from supply, to find ones that was accurate enough for them. The request was always honored by supply, as a matter of policy. BTW, one on each wrist, and two pocket types- one on a cord hanging from my neck and the "master reference" pocket watch in a holder above the scope. The bombing computer's time display was, in my opinion, about as accurate as a $10 Timex, not suficient.
...
From J Vega
They let me keep one, Andy... There is not much value in a years old used and well worn wind-up watch. Makes a nice rememberance, though. Also, I got to keep a couple of other things, like my dividers, "prayer wheel" (circular slide rule) and such well used stuff that they didn't want back. The Boluva multi function wristwatch I paid for, so of course it was mine to keep. Many crew members bought and paid for replacements for various issued gear, as some government issued things left a lot to be desired quality-wise. Bo Randall the knife maker got a lot of business that way. (gad, but those things cost a pretty penny)
-- http://www.wristwatchguide.com/wristwatch_history.html... Toward the end of the 1800s, women began to embrace the wristwatch as an item of adornment. ... Men tended to regard the wristwatch as effeminate. ... Despite the feminine association, the concept became accepted as indispensable to military campaigns as mechanization in war grew. The ability to read time with a quick glance rather than having to dig through pockets was critical in battle.
Officers in the South African Boer war (1899-1902) used wristwatches. ...
As demand for wristwatches in warfare grew, rugged timepieces covered with metal grids were introduced. ... luminous hands and markers were developed.
...
... the first Quartz clock in the late 1920s which was considered the most accurate time keeping device yet developed.
Still, the technology to allow use of Quartz crystals in wristwatches had to await invention of the integrated circuit in 1970. This enabled a Swiss group to manufacture the first commercially available Quartz watch ... The Swiss, however, ... were reluctant to pursue a technology that could crush Swiss dominance in less precise mechanical watches. ...
...
_Watch: electric electronic design_ book by Pieter Doensen ``covering the technical and historical development of the modern wrist watch ... the development of the electric and electronic wrist watch in historical perspective ''
``The Brave New World of Instrument Watches'' by Carlos A. Perez http://www.timezone.com/article.aspx?id=cjrml&articleId=cjrml0026
``Omega Speedmaster Professional X-33 ... [for] aviators ... The large distinctive central LCD screen features a large curved digital readout. ... optimized to permit reading of the display without having to remove one's hand from the flight controls. ...
... instrument watch design principles ...
...''
DAV: elsewhere I've heard ``Highly polished stainless steel behind enemy lines is not so attractive'' [FIXME: perhaps some of this is general enough to move to 3d_design.html ]
[I've seen someone else suggest sharkskin for a diving watch] links to``There are base metals, in which the metal costs much less than the machining and finishing, and precious metals, in which it costs much more. The most common base metals used for watches are stainless steel (SS) and titanium (Ti). Aluminum is sometimes used, but it's really too soft. ... The weight of a watch is very important if it gets much above about 100 grams. At that point you start to feel the watch ... titanium, which is much lighter than steel. ... gold, which weighs even more than steel
...
... crystals ... usually sapphire, which is a synthetic material right next to diamond on the hardness scale ... Less expensive watches use mineral glass, which is glass that's been coated to make it more resistant to scratching. The cheapest watches use acrylic plastic...
... If you're going to swim or dive with the watch, you want a bracelet or a strap made of nylon or rubber.
... ''
``The ergonomic implications of the anatomy of the wrist, On wearing a watch'' http://www.timezone.com/article.aspx?id=archives&articleId=archives0073 ``The under surface of the case should be matt rather than polished smooth/exhibition-back. This makes it less likely for the case to stick to the skin -- especially important in warm climates. ... Here, a matt titanium finish is the ideal case/bracelet material''
What! Quartz Tuning Forks? http://members.iinet.net.au/~fotoplot/accqf.htm has a picture of the quartz crystal used nearly all electronic wristwatches today, and a formula for calculating the vibrating frequency of a cantilever.
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
DAV finds this fascinating. Earlier mechanical watches are far more complicated (many more moving parts), and yet this watch is apparently more accurate (60secs/month). Later digital wristwatches are also far more complicated (at least the sliver of silicon is ... irreparable), and yet this watch is far more repairable than either mechanical or digital watches (assuming one can get transistors ...)``Accutron watches are unique in that they were the first electronic watches to dispense with the traditional "balance wheel and hairspring" as used in mechanical watches and other early battery powered watches. ... They are inherently more accurate than balance wheel watches for a number of reasons.
... Repairing and adjusting tuning fork watches is considerably easier...''
The ``magnetic gear'' of the Omega Cal. 1220 (Megasonic) is also interesting.
the (1 transistor) schematic diagram for this early electronic watch:
214 Circuit, Later Type 2 wire
V+
+ |
-----
--- 1.35 V battery
|
GND
V+ V+
| |
| |
L1 L2
| |
| |
| |/c
+--R--+--|npn
| 2M2 | |\e
| | |
+--C--+ |
220nF |
GND
L1 = feedback coil, approximately 1.5 KOhm
L2 = drive coil (actually wound in 2 parts),
approximately 11.5 Kohm.
crudely rendered into ASCII by David Cary 2002-11-22
based on
http://members.iinet.net.au/~fotoplot/acctech214.htm
218 Circuit
V+
+ |
-----
--- 1.35 V battery
|
GND
V+ V+
| |
| |
R1 |
2M2 |
| |
| |/c
+--R2----|npn
| |\e
| |
+--C----L1-+
220nF |
L2
|
|
GND
R2 = 0R, 3K3, 4K7, or 6K8, depending on type of transistor
L1 = feedback coil, approximately 1.2 KOhm
L2 = drive coil (actually wound in 2 parts),
approximately 10.95 Kohm.
crudely rendered into ASCII by David Cary 2002-11-23
based on
http://members.iinet.net.au/~fotoplot/acctech218.htm
Omega Cal. 1220 (Megasonic) Circuit
V+
+ |
-----
--- 1.10 V to 1.55 V battery
|
GND
V+ V+ V+
| | |
C R=470 KOhm |
| | L1
+---------+ |
| |
+------------+
R | |
| |/c |
+--| pnp |
| |\e |
| | |/c
| +-----|npn
| | |\e
R R |
| | |
GND GND GND
L1 = combination drive coil and sense coil.
crudely rendered into ASCII by David Cary 2002-11-22
based on
http://members.iinet.net.au/~fotoplot/acctech720.htm
The Amazing Bulova Accutron by Sean Connor http://www.elektron.demon.co.uk/accutron.html has a much more detailed "How it works" Page, with voltage waveforms and everything.
``... Two thousand turns of one coil (L2) are used as a sensing winding with the remaining 14000 turns serving as the impulse coils (L0 and L1). ...
... assume that C0 is charged and that R0C0 >> 1/Fo where Fo is the natural frequency of oscillation of the fork (Fo=360 Hz). ...''
Mark Headrick ``photos of a Bulova Accutron 218 watch (circa 1974) as it was disassembled.'' http://www.abbeyclock.com/photos/accutron.html has some very nice photographs.
... [FIXME: schematic]
see also #GeoClock Things to consider for my sundial:
Q: How far away from tulsa is the center line of longitude for my time zone ?
more sundial information:
Shadows is a Freeware which allows one to create its personalized sundial, for a specific location and orientation. The program prints the drawing full-sized on several pages if necessary, provides the template of the style that you just need to cut, and provides the co-ordinates of lines for the drawing of large sundials.
The shape of the analemma on Mars http://www.ogre.nu/doodle.html
The changing shape of the analemma on a hypothetical planet http://www.ogre.nu/analemma.htm
http://www.globalspy.com/Rennes-le-Chateau.htmlThese surprising windows have a distinctive characteristic which can be observed and photographed on a fine winter's day. The sun's rays, low on the horizon, pass through the patterns of the stained-glass windows at precisely midday by the sun, and project onto the opposite wall a tree covered with round fruit resembling apples. While the image, initially blurred, becomes more focussed, while moving from left to right, the fruits ripen as one watches, arid become red, except for three of them, which remain blue.
... Rennes-le-château.
moondials
But we do not experience eclipses every two weeks. This is because the plane in which the Moon orbits the Earth is inclined by about 5 degrees to the plane of the ecliptic (in which the Earth orbits the Sun).-- http://www.inconstantmoon.com/cyc_ecl2.htm DAV: so, this means the moon travels about 24° + 5° = 29° N of the equator, and sometime later the same amount S of the equator, right ? .
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).
Although we engineering and programming bears tend to think of time as an inherent part of the universe, it's actually a political construct and, as with all things political, subject to change essentially without notice.
- Radio Controlled Clocks and Watches in the US are now referred to as 'Atomic Clocks' and 'Atomic Watches' because of the leadership of Atomic Time and its corporate name.
- Atomic Time is the leader in Atomic Time Keeping technology and has over 200 different Atomic Clocks and Watches from Industrial Atomic Clocks to Atomic Watches for the consumer. Our price range is from $20 to over $2000
- Atomic Time is the distribution partner for Junghans, established in 1861 and with over 3000 Patents. We feature a strong line of high-class Junghans Carbon and Ceramic watches.
Tachyons, Time Travel, and Divine Omniscience
[FIXME: #free_will]One especially intriguing case in point concerns, in philosophy of science, the possibility of tachyons and time travel and, in philosophy of religion, the relationship between divine foreknowledge and human freedom. It is rarely appreciated by discussants of these respective issues that the problems are quite parallel and that insights garnered in the resolution of the difficulty in one discipline may have provocative implications for the solution of the parallel problem in the other field.
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
d.cary@ieee.org.