Q:

How are the SI units "generalised"?

How exactly are the SI units generalised from their definitions? 

E.g. the kilogram is a weight of an object of cylindrical form, with diameter and height of about 39 mm, and is made of an alloy of 90 % platinum and 10 % iridium..
http://www.bipm.org/en/bipm/mass/ipk/

How do units such as these generalise to other materials, shapes and dimensions?
How is it done?

A:

The definition of the kg is the mass of a particular lump of metal in Paris. 
The quote is trying (rather clumsily) to show that this isn't a very good definition because you can't make your own kg from any official definition. There is an almost complete project to replace the historical lump of metal with a new definition based on a physical effect that can be reproduced anywhere.

