I was reading about [gold number](https://en.wikipedia.org/wiki/Gold_number) and a book defined gold number as following: 

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> It is the minimum mass in milligrams of a stabilizing agent which is added to the 10 mL of red gold sol to protect it against coagulation caused by 1 mL of 10% (by mass) NaCl. 
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Is this the definition? Because I am not able to understand above definition.
Is NaCl used as the standard?