How Comes The Prestashop Currencies?

[hyyu]

I am trying to build an online store with Prestashop, and it comes a question from financial department.

I know that I can simply update the newest currency rate automatically in the "Currency rate section", but how the currency rates come?

 

There are different currency rates in different countries, different banks, even different companies.

And Which currency rate standard is Prestashop follow?

Our financial department is really  concerned about how the currency rate numbers come.

Please kindly give me a hint if anyone know the rules, thank you : )  

 

[ozdemir]

http://www.xe.com/

 

look:

http://doc.prestashop.com/display/PS16/Currencies