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Science

Pendulum Clock with Atomic Precision 213

Posted by CowboyNeal from the technology-misappropriation dept.
u19925 writes "Now you can get atomic clock precision out of your grandma pendulum clocks. Here is how it works: There is a camcorder fitted inside the clock which monitors the pendulum swing. It has an atomic clock signal receiver. It compares the pendulum swings with the atomic signal hearbeat. The camcorder also has an arm. If the pendulum clock drifts, then it uses its arm to push or pull the pendulum to make correction." It's not an April Fool's joke, but it is rather impractical.
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Pendulum Clock with Atomic Precision More

Pendulum Clock with Atomic Precision

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  • Regularity? (Score:5, Funny)

    by rjch ( 544288 ) on Thursday April 03, 2003 @11:17PM (#5658265) Homepage
    Now if we could just invent something that would push or pull Grandma when she's not regular enough...

  • Here's the link (Score:1, Redundant)

    by angle_slam ( 623817 )
    It would be nice if the submitter placed a working link [newscientist.com] to the article in question.

  • Why not magnets? (Score:5, Interesting)

    by FyRE666 ( 263011 ) on Thursday April 03, 2003 @11:17PM (#5658269) Homepage
    Why not just control the swing with a couple of magnets mounted at the ends of the pendulum's arc? It would surely be cheaper and easier to maintain than a camera and mechanical arm ;-)

    • Re:Why not magnets? (Score:4, Insightful)

      by deadsaijinx* ( 637410 ) <animemeken@hotmail.com> on Thursday April 03, 2003 @11:19PM (#5658292) Homepage
      you're right, magnets would be easy/more cost effecient. however, Cameras and robot arms are sooo much cooler.... 0_O

      okay, the real question is why do this at all?

      • I'm a self professed 'gadget junkie' and love playing around with robots and stuff, but this idea is just, well lame. And irrelevant. As if you are going to notice that your clock is out by 1/100 of a second. I don't know why you'd even bother. I know this sounds negative et al, but zzZZZzz.

      • Re:Why not magnets? (Score:5, Funny)

        by scott1853 ( 194884 ) on Friday April 04, 2003 @12:10AM (#5658529)
        okay, the real question is why do this at all?

        Geez Batman, how are we going to figure this one out?

        Quick Robin, to the article!

        There is a growing shortage of people who are familiar with the workings of the large mechanical clocks on churches and public buildings, as routine maintenance tasks such as winding the clocks become automated. Yet they still need to be put forward an hour in spring and moved back again in the autumn without damaging their fragile mechanisms, some of which are 250 years old.
        • There is a growing shortage of people who are familiar with the workings of the large mechanical clocks on churches and public buildings, as routine maintenance tasks such as winding the clocks become automated.

          Heck, there is a growing shortage of people who can set the clock on the camcorder needed to adjust the timing of their pendulum clock!
        • "Yet they still need to be put forward an hour in spring and moved back again in the autumn without damaging their fragile mechanisms, some of which are 250 years old. "

          Cheaper/easier solution: Put a big honking neon sign below the clock that says "[name of time zone here] Standard Time." Require other people to remember to add an hour for "summer"/"daylight" time when appropriate.
      • Clearly having clocks that are off by a few minutes isn't acceptible anymore. This is why many clock towers in England, including Big Ben [clockpost.com] in London, are converting to digital read-outs. The thinking behind these renovations is that instead of retrofitting the current clock systems with reliable electric motors, the entire system should be modernised. And why not?

      • Re:Why not magnets? (Score:3, Interesting)

        by hlee ( 518174 )
        Richard Feynman once observed a flying spinning/wobbling paper plate with a motif on its side, and doodled a surprisingly complex mathematical equation describing its behaviour. When questioned later - WHY??? Hell, because it was fun! Of course, this did lead to his seminal work on quantum mechanics, and a nobel prize.

        Sure this pendulum thing seems kind of silly, but may be the feedback mechanism could inspire some new neural network neuron - a precursor to true AI!

        You could be just trolling asking a ques
        • Once read an article in Analog magazine (you know the one with the rivits) in the Alternate view section about some very small value of G (gravity) using pendulms ime thinkith it was around 1985 but I could be wrong

      • Re:Why not magnets? (Score:3, Insightful)

        by asreal ( 177335 )
        There are some people who are just as obsessive about clocks as the gamers are about frames per second and neon caselights. Just like a gamer will rig up a cooling system and modded case that seems utterly useless to a normal person , a clock geek will go through great pains to have a cool, accurate clock. Personally, I think I'd rather have a grandfather clock with a camcorder and robotic arm than a tricked out computer system. But that's just me.
    • Simply nudge the clock base vertically (pikc a corner/side) as required, by a small system of active mounts, that sense the pendulum's momentum and urge correction? Banging on the weight as it swings seems a bit counter-productive.

    • Re:Why not magnets? (Score:5, Interesting)

      by Zeinfeld ( 263942 ) on Thursday April 03, 2003 @11:29PM (#5658352) Homepage
      Why not just control the swing with a couple of magnets mounted at the ends of the pendulum's arc? It would surely be cheaper and easier to maintain than a camera and mechanical arm

      These are not grandfather clocks, they are large public clocks and the movements are very old. The objective is to avoid human contact since people tend to break them advancing or retarding them for summertime.

      So this is not a Rube Goldberg device, it is a piece of conservation technology :-)

      The Westminster Tower Clock, with its famous bell 'Big Ben' is kept accurate by a warden who runs (ok shuffles, most jobs of that type go to aged war veterans) up a flight of stairs and adds or removes pre-decimal pennies from the pendulum bob. Ah you cry, but the time taken by a pendulum does not depend on the weight, well yes but the pennies slightly raise the center of gravity of the bob you see...

      The camera bit sounds a little over the top, surely an led and a receiver???

      • Re:Why not magnets? (Score:5, Interesting)

        by unitron ( 5733 ) on Friday April 04, 2003 @01:08AM (#5658757) Homepage Journal
        "The camera bit sounds a little over the top, surely an led and a receiver???"

        I'm guessing that you mean an opto-isolator type circuit. Other possibilities, a magnet embedded in the pendulum and a hall-effect device near each end of the path of the swing or a coil attached to a circuit which will detect the inductance change caused by the pendulum's proximity, or just let the pendulum brush across a contact pair and complete a circuit.

        • I think he wants to sense the position of the pendulum by having a led in front of the pendulum and an receiver in back, placed in such a way that the pendulum does not always block the signal... with some signal conditioning, you would have a nice digital signal that says 'the pendulum is here/not here'

          i wouldn't classify that as an opto-isolator type circuit, but i suppose you might

      • Re:Why not magnets? (Score:2, Informative)

        by NegativeK ( 547688 )
        Ah you cry, but the time taken by a pendulum does not depend on the weight, well yes but the pennies slightly raise the center of gravity of the bob you see...

        Slightly off-topic, but interesting none the less: a normal pendulum does not take the same time to reach the bottom no matter where it is released, contrary to popular belief. The correct curve is actually an inverted cycloid, and the finding of this curve was deemed the 'tautochrone problem.' Obligatory mathworld linkage: Tautochrone Problem. [wolfram.com]
        O
      • The camera bit sounds a little over the top, surely an led and a receiver???

        The original article makes no mention of a camera -- this appears to be sloppy summarizing on the submitter's part. The article says it's done with "infrared sensors", which sounds saner.

        That's /. for you. Even the submitter hasn't read the article.

      • Take a couple of pictures around the expected time, see which way it is moving and how close to optimum. Magnets, LEDs, now you are talking special circuitry. Webcams are simple and cheap.
      • These are not grandfather clocks, they are large public clocks and the movements are very old. The objective is to avoid human contact since people tend to break them advancing or retarding them for summertime.

        So this is not a Rube Goldberg device, it is a piece of conservation technology :-)

        Why not eliminate the Rube Goldberg device and get to the root of the problem: Eliminate DST [standardtime.com]

        • Farmers hate it. It greatly screws with them having to get up with the sun, then deal with customers that arbitrarily
        • Until people adjust their work and school schedules to conform to sunrise and sunset times, you are still going to get people who wake up at 7 and go to bed at 11. If we can timeshift an hour of daylight from before dawn to before bedtime, we will save in North America 36,000,000 kWh of electricity per day.
          (based on as assumption that 300,000,000 people each leave 2 60W bulbs burning when they are awake at night). You can quibble about the numbers if you want, but the point of a massive energy saving is the
    • To my thinking it would be rather difficult to account for the timing and duration of the electomagnet, given that as the pendulum moves, the magnetic field's pull on it changes constantly. At least with this method, you have a set force that can be applied to the pendulum in order to correct it, which makes the programming a whole lot simpler.

    • Re:Why not magnets? (Score:5, Insightful)

      by wwwillem ( 253720 ) on Friday April 04, 2003 @03:43AM (#5659232) Homepage
      We are used to /.-ers commenting without having read the article. That's even the fun of slashdot. But it appears that we have reached new levels: even people submitting a topic don't read their source anymore and everybody else follows like lemmings.

      The New Scientist article doesn't mention any camera's, camcorders (why should you record this anyway, it's over in a second :-), or such. According to the article, the guy just uses a couple of IR sensors. That's a whole lot cheaper than camera's.

      Still, this whole project is of course nuts. You love clocks (like I do !!) and than you have the honor to wind them every day, every Sunday at noon, or ..... That's just the fun of having old clocks.

      Anybody can read the time from his cellphone. And using a GPS for the time-reading ... why doesn't the guy put a GPS on the pendulum and measure the frequency that way. That's cool!!!
    • Umm, why not install a tiny, free, dial up the atomic clock dial-up app on your computer and hand adjust the time on the clock every week or so... considering that, given the dial split up into 60 sections nature of the clock dial, at best you are reading the time on the clock at an accuracy no better than to the half minute (give or take?)


      'Cause that's just not geeky.

  • New low for /. (Score:1, Offtopic)

    by genka ( 148122 )

    Editors forgot how to insert links.
    Any "HTML Programmers" care to help?

    • Re:New low for /. (Score:1, Offtopic)

      by geekoid ( 135745 )
      umm, I don't think it was the editors that wrote the post. They just posted it. I believe it has always been there policy to not change the original content of the person who submitted. Of course, a link where they posted there comment would have been nice.
  • heres a revised version of the article:

    Now you can get atomic clock precision [newscientist.com] out of your grandma pendulum clocks. Here is how it works: There is a camcorder fitted inside the clock which monitors the pendulum swing. It has an atomic clock signal receiver. It compares the pendulum swings with the atomic signal hearbeat. The camcorder also has an arm. If the pendulum clock drifts, then it uses its arm to push or pull the pendulum to make correction. " It's not an April Fool's joke, but it is rather impract
  • "Now you can get A HREF="http://www.newscientist.com/news/news.jsp?id =ns99993549">atomic clock precision out of your grandma pendulum clocks.

    Sigh. I'd love to get a href, but where would I put it?
  • how about that hyperlink :\
  • Comment removed based on user account deletion

  • Rube Goldberg (Score:4, Funny)

    by Drachemorder ( 549870 ) <<brandon> <at> <christiangaming.org>> on Thursday April 03, 2003 @11:19PM (#5658279) Homepage
    Is this real science, or the results of this year's Rube Goldberg contest?

  • Erm... (Score:1, Redundant)

    by Tailhook ( 98486 )
    Wow.
  • Not an April Fool's link, but it is rather impractical.

    Try this [newscientist.com]

  • I was going to do this (Score:5, Interesting)

    by Zeinfeld ( 263942 ) on Thursday April 03, 2003 @11:20PM (#5658294) Homepage
    Actually this was a project I had in mind, but it can be done with much less kludge.

    My plan was to put a magnet on the pendulum and then put the regulation mechanism on the reverse. This would measure each swing of the pendulum from the emf induced in a coil on the back of the clock. This would also be used to advance or retard the pendulum if necessary.

    • No you werent (Score:4, Funny)

      by stratjakt ( 596332 ) on Thursday April 03, 2003 @11:52PM (#5658445) Journal
      You never even thought of it until just now.

      C'mon, admit it.
    • Scientific American did that in their Amateur Scientist section about 45 years ago. The WWV receiver used tubes, but they had two fingertip-sized transistors driving the electromagnet. I considered building one for my junior-high science fair, but built a four flip-flop "computer" instead. Eight transistors, cost me about 5 bucks each. That was about a day's worth of my father's income.

  • ...is there to prevent posters from making glaring errors in their submissions.

    (Use the Preview Button! Check those URLs! Don't forget the http://!)

    Maybe the editors should get one of those too. It's pretty handy for us peons who make mistakes all the time...

  • This just in ... (Score:1, Funny)

    by Anonymous Coward
    Amazon has patented hyperlinking, so from now on ... you'll have to form your own links....
  • Perhaps Slashdot needs an atomically-precise HTML checker to catch those pesky "a href" tags.
  • For more information on pendulum clocks, check out A HREF="http://science.howstuffworks.com/clock.htm"> this site :P

  • Latency? (Score:5, Insightful)

    by shibbydude ( 622591 ) on Thursday April 03, 2003 @11:25PM (#5658333) Homepage Journal
    Wouldn't the latency of the net connection/camera/lever defeat the whole purpose of atomic precision? I mean, anyone can just reset thier clock once and a while to the "technical" standard time. Is this really accurate?

    • Re:Latency? (Score:5, Interesting)

      by AndroidCat ( 229562 ) on Friday April 04, 2003 @12:15AM (#5658541) Homepage
      The most accurate clock I have is an ancient "digital" flip-leaf that depends on the powerline 60 Hz for its time base. It's not very precise because the line freq does drift from time to time. However, once it drifts too far, the the power company applies a correction to bring it back into range. Accurate, but not precise.

      My computers and other appliances use crystal clocks which are very precise. But they slowly drift, and no correction is applied (except when I net sync my computer) so they drift and keep on drifting. Precise, but not accurate.

      The net connection/camera/lever arrangement may not be as precise as an atomic clock, but it will be very accurate. See how it works? ;^)

      • Re:Latency? (Score:4, Interesting)

        by cant_get_a_good_nick ( 172131 ) on Friday April 04, 2003 @12:53AM (#5658705)
        I seem to recall an article recently that some clocks in Brazil were off becuase the line wasn't up to snuff. I think the power was off so much that some cycles weren't being counted, so the clocks ran way slow.

        Then there's the story about the engineering students that noticed their professor never wore a watch, so they rigged something up to the power line to alter its frequency. They ran the clock fast he kept talking faster and faster to keep pace with the clock. I forgot how far they got before he noticed, but from what I remember, they had him compressing the class pretty much.

        • Re:Latency? (Score:4, Funny)

          by 2nd Post! ( 213333 ) <gundbear.pacbell@net> on Friday April 04, 2003 @04:13AM (#5659312) Homepage
          Haha, that was a story we tell at Caltech about how we did that to one of our profs. It was a math prof I think.

          Date: Tue, 14 Dec 1993 13:50:47 PST
          From: hcate.OSBU_North@XEROX.COM
          Subject: Life 3.9 A collection of clean humor gathered on: 16 Jun 88

          I got this from the June issue of "Discover".... ...Among science students Caltech is the capital of retaliation. A
          particularly satisfying incident in the early 1970's involved a math
          professor who annoyed students by his mechanical, predictable
          approach to teaching - his lecture notes were straight from his
          book. One student got hold of a device that changed the normal
          frequency in an electrical outlet to any desired value. He plugged
          the classroom clock into it and, over serveral weeks, upped the
          speed -first by 10 percent, then 12.5 percent, then 15 percent.
          Each day the frazzled professor raced through the tried-and-true
          lecture faster and faster, until finally he was reduced to
          fast-forward gibberish.
        • so they rigged something up to the power line to alter its frequency

          School clock systems (at least back in my day :^) used a central signal with the power line as a carrier. Once a minute the cental time clock would send a signal to advance a minute. There was also a reset and advance hour signal so they could fix borfed clocks and leap forward/fall back.

          Add a line filter to the clock, inject your own signals, piece of pie!

          As for Brazil, they're in a bad way. That sort of variation shows that they're no

      • I don't think the power company applies a correction so much as it tends to drift above 60Hz about as often as it drifts below 60Hz so it all evens out.

        Sometimes two wrongs do make a right. On average.

        • I don't know about the US, but in the UK the power company are required to make the total number of cycles in a day come out pretty close to right (weak memory says withing one second) but allowed larger margins of error within the day So yes, they do positively intervene to correct the number of cycles per day.

    • OK, let's assume a worst-case latency of 1 second. Even with that extremely pessimistic assumption, you've still got a clock that is never more than a second off. Hell, assume that it doesn't actually adjust the pendulum until it's 3 seconds off; you've still got a timekeeper that will never be more than 4 seconds wrong. For an antique analog clock, you'd be crazy not to take that.

      Compare that to my wristwatch, which is a far more capable timer than a pendulum clock. Even a quartz clock drifts over time;

    • Re:Latency? (Score:2, Interesting)

      by YouAreNotTheBest ( 584423 )
      Don't you people read the article???? huh..

      From the article:

      "If the antique clock loses time, a small piston speeds it up with a gentle nudge on the pendulum; if it runs fast, the piston slows it down. Each day, the clock is kept accurate to a tenth of a second. "

      duh... don't think that the precision is atomic..

      what a crappy title?? "Pendulum clock with atomic precision"
      also crappy description about camcorders and stuff that are never described..

      the idea of this system is to prevent antique clocks from

  • It's not atomic precision.. (Score:3, Insightful)

    by Tikiman ( 468059 ) on Thursday April 03, 2003 @11:42PM (#5658402)
    It's 1/10 second precision that get synced daily to an atomic clock - a pendulum clock with "atomic precision" doesn't even pass the sniff test
  • This time, I actually read the article, and it's insanely funny!

    I'm not sure why. Probably because it's British.

  • This was in Scientific American (Score:3, Interesting)

    by TerryAtWork ( 598364 ) <research@aceretail.com> on Friday April 04, 2003 @12:08AM (#5658519)
    About 20 years ago - only they used the mechanism from a quartz clock.

    • Yes, maybe even more than 20. If memory serves, it used a magnet to tug on the bob once a second, which had the effect of locking the pendulum oscillation to the quartz crystal circuit. A gentle tug will do it -- the forces that cause drift are small, subtle and easy to overcome.

      I've been fantasizing about updating this for modern technology, using the pulse-per-second output from a GPS receiver. You could even graft this on to the quartz system, using the quartz crystal as a temporary backup for when the
    • I remember this, too. Actually, with today's technology, I think using a radio receiver would be easier to implement than the clock and the physical user interface.

      It always amazes me how people always invent ideas that have been around for a while. Temporal chauvanism!! ;-)

  • RTFA people (Score:5, Informative)

    by glenebob ( 414078 ) on Friday April 04, 2003 @12:20AM (#5658567)
    Doesn't anyone read the friggin articles?

    Nowhere in the article are the words 'camcorder', 'grandma', 'arm', etc.

    It wasn't designed to fit into a grandmother clock and it certainly doesn't use a camcorder. It uses an infared sensor to sense pendulum location and a 'piston' to modify pendulum swing, and it is being used to automate maintenance on large clocks in churches, etc. It can also set the clock ahead and back an hour for daylight savings time.

    Gotta be the worst case of can't be bothered to RTFA I've ever seen.

    Now, anyone who thinks it would be better to replace the clocks in Big Ben with some modern electronic thing... well... probably ought to be shot. This doesn't seem like a bad way to get those big clocks to operate a good long time without human intervention.

  • This is awesome... (Score:5, Funny)

    by Polyphemis ( 450226 ) on Friday April 04, 2003 @12:29AM (#5658608)
    Sweet! Now the 'tick-tock-tick' my grandma hears every day of her life ominously counting down to her impending death can be atomically accurate! Thanks Slashdot!

  • We are the borg... (Score:4, Funny)

    by Znonymous Coward ( 615009 ) on Friday April 04, 2003 @12:32AM (#5658622) Journal
    Our clocks are perfection... Resistance is futile.

  • Not as impractal as it first looks (Score:5, Informative)

    by Chronos56 ( 652646 ) on Friday April 04, 2003 @12:33AM (#5658627)
    I feel that some informed comments are required for this topic. I am a clockmaker, yes I work on 200 year old clocks all the time; and I have to say that this is a really neat merging of modern and antique technology.

    The clocks that are being regulated are tower clocks, they are observed by hundreds if not thousands of people a day. It would be nice to know that they are on time. It would also be a crime to rip out the old pendulum movement and replace them with an electric movement. Another feature is that the old antique system can run for several days in the event of a power failure, it just won't be quite as accurate.

    The movements in these clocks are heavy cast iron units with large gears and very heavy pendulums. Using a magnet system to attempt to influence the timing rate would probably prove ineffective. However using some sort of system to raise or lower the pendulum by just a couple of millimeters will affect the timing rate by several seconds a day.

    These clocks used to be wound once a week by hand and the time would have been reset at that time. These days most of these clocks have been converted to an automatic winding system, thus they see much less hands on maintenance, automatic systems for regulating the clock become much more attractive.

    As a side note, the tower clock in London, commonly known as "Big Ben" ("Big Ben" is really the name of the bell that is used to count the hours) is regulated by adding or removing one or two old English Pennies, the one that were about the size of an old American Silver Dollar. The clock is regulated to be as on time as possible on the Queens Birthday and on New Years Eve.

    Going even further afield some of you might get a kick out of the elaborate astronomical clocks that were designed in the 1800's. These were astonishing pieces of engineering that have been known to take an astronomer to figure out all of the settings required to set the clock.

    I guess my passion for my vocation is showing, I hope that I was able to add something of interest.

    Chronos
  • Uhh, it may just be me, but isn't the atomic receiver the one doing the time telling? I mean, you're using a clock to run the pendulum, whereas the order used to be reversed. (Pendulum ran the clock)

    Does that seem really frivilous to you too? This barely fits under "Stuff that matters"

  • Hope no one uses these clocks... (Score:3, Funny)

    by Cs.Ender ( 615148 ) on Friday April 04, 2003 @01:03AM (#5658743)
    From the article:
    The piston will gradually stop the pendulum over 20 swings or so, avoiding any sudden forces. Then, 11 hours later, when it will be 1 pm British Summer Time, the piston will gently set it ticking again

    So if lightning strikes the clock at 8:00 am, it will be stopped at 1:00, and no one will be able get their time machine back to the future...

  • Ultra-accurate mechanical clocks (Score:5, Interesting)

    by Wesley Felter ( 138342 ) <wesley@felter.org> on Friday April 04, 2003 @02:04AM (#5658955) Homepage
    Danny Hillis designed the Clock of the Long Now [longnow.org] to keep time accurate to the second for 10,000 years, and it's completely mechanical.
    • Where do you get "one second in 10,000 years"?

      When the clock first was announced, I remember reading that the point of it was not to keep accurate time, but to figure out how to create a device that could operate continuously for 10,000 years, surviving the changing social, political, technical, economic, and sociologic landscapes.

      Today, after reading the site at length it seems they are using a traditional oscillator steered by the rotation of the earth. That's many orders of magnitude less accurate tha
  • I read this as Pentium Clock with Atomic Precision

    So I'm thinking to myself, why would someone make a clock with a Pentium in it? What would be the point? Some kind of wi-fi enabled clock that turns on the wi-fi enabled coffee machine in the morning?

    Then my brain woke up....

  • In answer to the people who suggest (electro)magnets, a design to do just this was published long ago, before the 1993 archive start, in dead tree Scientific American. Assuming the pendulum weight is cast iron, it is perfectly practical to use a magnet. As I remember it, the magnet goes on the dead center line below the pendulum bob. Depending on where in the cycle it is turned on briefly, it will accelerate or decelerate the pendulum very slightly. I guess with some clocks if you made the magnet big enough

  • Camcorder? (Score:3, Informative)

    by nmg196 ( 184961 ) on Friday April 04, 2003 @05:13AM (#5659434)
    Camcorder - where on earth did he get that from?! Did the guy that submitted that actaully read the article he was submitting?! It doesn't mention that in the article - mainly because it would be a stupid idea. That's maxiumum overkill if I've ever heard of it. That would be like using a camcorder to 'look' and see if the fridge door is shut!

    And why use a piston to change the swing? What's wrong with an electromagnet which wouldn't need to actually touch the pendlum?

    Nick...
  • Do you REALLY need an atomic clock to get precision within 0.1 second/day?

    Seems like a quartz would do better than that!

    Overengineered.

  • Synchronizing a clock with another one is hardly new. Any raido-controlled clock does it. And it does not give you a "Pendulum Clock with Atomic Precision" at all. It gives you a slaved pendulum that is still pretty imprecise but gets resynchronized when the imprecision reaches a rather large value. For short term usage that means it is just as preice as it was before.

  • you could just buy a clock that receives the atomic radio signal....
  • Now you can get atomic clock precision on your computer too! Much like the 'atomic clock accuracy on a pendulum clock' seen on /., the atomic clock on your computer is "set" by using the ntp protocol. Wow!

  • Conceptually.... (Score:5, Informative)

    by wowbagger ( 69688 ) on Friday April 04, 2003 @09:09AM (#5660078) Homepage Journal
    Conceptually, this is the same trick almost ALL accurate clocks use - it's called "discipline".

    Consider where I work - we have a very accurate 10 MHz reference to sync all our RF gear to. We need that ref to be tracable to the National Bureau of Standards. Now, it would be somewhat impractical to check with the Bureau 10 million times a second (anybody want to run a fiber from Boulder to Wichita just for the time sync?).

    Before I go on, let me point out the difference between precision, accuracy, and repeatability.
    • Precision is how many decimal places you can put on a reading. Saying "it's 12:00" is not as precise as saying "it's 12:00:00.0001".
    • Accuracy is how close you are to the right answer. Saying "it's 12:00:00.001" is not as accurate as saying "it's 13:00" if in truth it really is 13:01.
    • Repeatability is a measure of how close you are to your previous readings - if you say "it's 12:00:00.0001", "It's 12:00:01.035","It's 12:00:01.002" when read several times in one millisecond, then you aren't very repeatable.

    From a metrological standpoint, having more accuracy than repeatability is useless. Having more precision than accuracy is also useless. (Ignoring tricks like averaging for the moment.)

    Back to the example. What we do is to have a very high precision and stable oscillator (we used to use a rubidium standard). It has a long term stability of about 10E-9 and a short term stability of 10E-12. In other words, over a short period of time the thing will drift not more than one part per trillion, and over the long term (days) it will drift about one part per billion.

    Now, that is running next to a GPS receiver that gives us a time tick synced to the Bureau. Every second the GPS time is compared to the local time standard, and an error value is computed. That error value is averaged over a long period of time, and used to gently tweak the rubidium standard. Thus, over the long run the drift is reduced to level of the cesium clocks, about 10E-13.

    So we have atomic clock accuracy but rubidium clock precision and repeatability.

    Now, if you used the same sort of technique on a pendulum clock - measure the error between the clock and the GPS, average, filter, and apply - you would have atomic clock accuracy with pendulum clock precision. Granted, I would not want to use the clock's time for reporting astronomic phenomena where the precision must be very high, but for normal use this would be quite good enough.

  • That's the point! (Score:4, Funny)

    by docbrown42 ( 535974 ) on Friday April 04, 2003 @09:42AM (#5660230) Homepage
    It's not an April Fool's joke, but it is rather impractical.

    Well, that's the point, isn't it? I mean, what's the point of being a geek if you can't do geeky, pointless things?

  • to suggest that if one is going to go to the length of having a signal from an atomic whatsit, that one could far more simply DISCONNECT the pendulum and run the clock hands by the atomic clock, and just have a simple motor keeping the pendulum swinging away?

    Or is the tremendous effort to keep the weights/pendulum the 'driver/regulator' for the clock mechanism the point? Maybe I'm just a mechanical clock philistine.

  • WTF? (Score:3, Insightful)

    by SuiteSisterMary ( 123932 ) <slebrunNO@SPAMgmail.com> on Friday April 04, 2003 @11:13AM (#5660846) Journal

    That's not having an atomically precise clock; that's using an atomically precise clock to automatically adjust your not-so-precise clock.

  • Why do you need a camcorder? (Score:3, Interesting)

    by shylock0 ( 561559 ) on Friday April 04, 2003 @11:57AM (#5661238)
    The camcorder seems a little extravagant. Why not just use an induction loop (a la EZ-Pass or bicycle spedometers) to sync the pendulum with the atomic clock?
  • It's an atomic clock with a mechanical "display".


    Does this mean that I've bred a superhorse when I put a race horse in a trailer and drive him cross-country at 80mph?


    Stupid headline detracts from otherwise neat hobby-hack.

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