Picture of the 2 lines on a platinum iridium bar

[fizagic]

Hello all,

The standard meter was said to be the distance between two scratches on a platinum iridium bar.

http://en.wikipedia.org/wiki/Metre

Where are these scratches? I only see the bar.

 

[Drakkith]

There doesn't appear to be a good picture on wikipedia. Perhaps some google searching would turn up something else?

 

[sophiecentaur]

I must say, I never thought of that before but those scratches will need to be VERY FINE for the standard length to be precise. You can probably only see them with a lens.
When they are used for making or calibrating a sub standard, they 'know' pretty well where to look for these tiny scratches because they already have a 'crude' 1m measure. They can't 'lose them'.

 

[AlephZero]

There is a better picture and some technical details here.
http://museum.nist.gov/object.asp?ObjID=37

 

[pmacias]

Hello, thank you for your question. The scratches on the platinum iridium bar that were used to define the standard meter are no longer visible due to wear and tear over time. The bar has been replaced with a more accurate and stable definition of the meter based on the speed of light. However, the original platinum iridium bar is still used as a historical artifact and serves as a reminder of the evolution and refinement of scientific measurements.