# How useful is the formal definition of the second, really?

**URL:** <https://boards.straightdope.com/t/how-useful-is-the-formal-definition-of-the-second-really/686370>\
**Category:** Factual Questions\
**Created:** [April 17, 2014, 11:25pm UTC](https://boards.straightdope.com/t/how-useful-is-the-formal-definition-of-the-second-really/686370 "2014-04-17T23:25:35Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![handsomeharry](https://avatars.discourse-cdn.com/v4/letter/h/e9c0ed/32.png) [@handsomeharry](https://boards.straightdope.com/u/handsomeharry)\
**Post date:** [April 22, 2014, 3:33am UTC](https://boards.straightdope.com/t/how-useful-is-the-formal-definition-of-the-second-really/686370/21 "2014-04-22T03:33:12Z")

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> [@cmyk](#):
>
> Wikipedia mentions that the best [atomic clocks](http://en.wikipedia.org/w/index.php?title=Atomic_clocks#Evaluated_accuracy) are precise in measuring its frequency up to 1 part in 10[sup]15[/sup].
> 
> That means it would only be off by about 1 second over 300 million years!

Oh, great! That means I have to reset my watch again in 300 million years! Thank for nothing!

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**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\
**Post date:** [April 22, 2014, 4:15am UTC](https://boards.straightdope.com/t/how-useful-is-the-formal-definition-of-the-second-really/686370/22 "2014-04-22T04:15:50Z")

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> [@handsomeharry](#):
>
> Oh, great! That means I have to reset my watch again in 300 million years! Thank for nothing!

Every now and then they have leap seconds. 😃

Understand, the second itself is the same duration, they just skip ahead or back one.

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**Author:** ![Hector\_St\_Clare](https://avatars.discourse-cdn.com/v4/letter/h/b5ac83/32.png) [@Hector\_St\_Clare](https://boards.straightdope.com/u/Hector_St_Clare)\
**Post date:** [April 24, 2014, 2:07am UTC](https://boards.straightdope.com/t/how-useful-is-the-formal-definition-of-the-second-really/686370/23 "2014-04-24T02:07:30Z")

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> [@TroutMan](#):
>
> But how do you calibrate it if you can’t actually get to 0 K? Wouldn’t it have been more useful to use an attainable standard like 4 K?

My background is not in physics (nowhere close) but I would assume that you look at the behavior as it gets close to 0 K, and extrapolate the limit.

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