Tuesday, February 26, 2013

Turkey Time, a Watch, and Accuracy

This article was originally posted in November of 2012 on 10GbE.net.


While waiting on the turkey yesterday I was flipping through the latest issue of Wired and stumbled across the new Seiko Astron watch, and my inner nerd started to swoon.  Now for the few of you out there who don't get Wired, especially the December issue, think of it as the geek version of the old Sears Wishbook. This time of year every tenth ad in the magazine is for a high end watch, its geek meets chic.  Among all the fancy watch ads, here was both an article and an ad for a Seiko, the brand my dad wore.  Dad worked outdoors every day of his life, never used a computer & swore by his Seiko, he considered it the working man's watch. So it was kinda funny seeing Seiko among ads for all the other high end brands from Rolex on down.

To be sure we're all on the same page let's first take a moment, and define accuracy.  Simply put accuracy, when talking about time, is the average deviation from reference time.  Today for high precision instruments accuracy is often measured in nanoseconds (1x10E-9 or billionths of a second) lost, or gained, each second or day. With 86,400 seconds in a day sometimes it's easier to use a day when dealing with really small numbers. National and international reference clocks use the excitation of Cesium atoms by microwaves then they measuring the frequency of the resulting emitted photons as the electrons jump energy states.  This process is so repeatable, that it was made the international standard for time keeping over 50 years ago.     

So what about this Seiko arose the geek inside me? Active GPS synchronization to the local time zone, and an understanding of all 39 time zones world wide.  This watch figures out where you are on the planet, then selects the appropriate timezone and resets itself to local time, all for only $2,300.  My smartphone has been doing the same thing since they first arrived, but that's a different story.  Seiko also claims the Astron has an accuracy of 1 second every 100,000 years, or 27 nanoseconds/day. By watch standards this is very accurate.  

So how does the Astron stack up to some real world high precision clocks?  Clock systems used in electronic financial markets typically use highly accurate clocks (1 picosecond/day internally) that are even more precise then Cesium clocks. To be in-step with the rest of the world though they must rely on our less accurate GPS system (10 nanoseconds/second), and often a pulse per second distribution mechanism which reduces this further to 25 nanoseconds/second (2 milliseconds/day).  As mentioned above commonly used Cesium clocks are accurate to 1 second ever 1,400,000 years or 2 nanoseconds/day. A new proposed standard clock would excite neutrons instead of electrons and thus be even more accurate, 1/20th of second every 14,000,000,000 years. Well there's the oven timer, it's accurate to a minute every six months when I reset it, the turkey's done. Happy belated Thanksgiving everyone… 

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