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