# SI units of measurement **URL:** \ **Category:** Factual Questions\ **Created:** [September 1, 2009, 4:16am UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446 "2009-09-01T04:16:54Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![ChrisBooth12](https://avatars.discourse-cdn.com/v4/letter/c/e95f7d/32.png) [@ChrisBooth12](https://boards.straightdope.com/u/ChrisBooth12)\ **Post date:** [September 1, 2009, 4:16am UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/1 "2009-09-01T04:16:54Z")
I have heard that the meter was once defined as a certain percentage of the distance from the pole to the equator. There was a rod that was used to be a meter and all other meters are based off the rod locked in the vault. Then it was decided that the rod might be changing and a set definition of the distance traveled during a certain time at the speed of light was used…Ok fair enough but then why cant we do a similar thing for the kilogram? I understand that a weight is still used and locked in a vault. Wouldnt a set definition be better then a tangible object? ---
**Author:** ![DanBlather](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@DanBlather](https://boards.straightdope.com/u/DanBlather)\ **Post date:** [September 1, 2009, 4:29am UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/2 "2009-09-01T04:29:10Z")
> [@ChrisBooth12](#): > > I have heard that the meter was once defined as a certain percentage of the distance from the pole to the equator. There was a rod that was used to be a meter and all other meters are based off the rod locked in the vault. Then it was decided that the rod might be changing and a set definition of the distance traveled during a certain time at the speed of light was used..Ok fair enough but then why cant we do a similar thing for the kilogram? I understand that a weight is still used and locked in a vault. Wouldnt a set definition be better then a tangible object? Just to be annoying, let me be the first to point out that the kilogram is a unit of mass, not weight. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 1, 2009, 4:30am UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/3 "2009-09-01T04:30:46Z")
The move to such a standard is already underway - see the section titled “[The Avogadro Project](http://en.wikipedia.org/wiki/Kilogram)” ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 1, 2009, 11:39am UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/4 "2009-09-01T11:39:13Z")
Particularly interesting from **beowulff** ’s link is the section [Stability of the International Prototype Kilogram](http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_International_Prototype_Kilogram), which talks about variation in mass of the Prototype Kilograms. The International Prototype Kilogram is just one of 40 replicas, that was selected (arbitrarily?) as The International Prototype Kilogram. ---
**Author:** ![nate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nate/32/13085_2.png) [@nate](https://boards.straightdope.com/u/nate)\ **Post date:** [September 1, 2009, 5:52pm UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/5 "2009-09-01T17:52:15Z")
I believe NIST is working on an electronic kilogram. I suspect other national labs are probably working on something similar. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 1, 2009, 5:53pm UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/6 "2009-09-01T17:53:15Z")
> [@ChrisBooth12](#): > > I have heard that the meter was once defined as a certain percentage of the distance from the pole to the equator. 1/10,000th. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 1, 2009, 6:00pm UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/7 "2009-09-01T18:00:51Z")
Thre was a fascinating article, I think in the summer of 07, about polishing silicon spheres for the Avogadro project. It appeared in Scientific American. ---
**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\ **Post date:** [September 1, 2009, 6:21pm UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/8 "2009-09-01T18:21:20Z")
> [@Joe Frickin Friday](#): > > 1/10,000th. No, it was 1/10,000,000th. If it were 1/10,000th, then it would be 10,000 metres, or about 6 miles, from the Equator to one of the poles. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [September 1, 2009, 8:16pm UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/9 "2009-09-01T20:16:43Z")
10,000 km rather, I’d say. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [September 1, 2009, 11:11pm UTC](https://boards.straightdope.com/t/si-units-of-measurement/508446/10 "2009-09-01T23:11:49Z")
> [@John\_DiFool](#): > > 10,000 km rather, I’d say. Which was **Giles** ’ point, right? 😉