How does it work exactly?

I belive there are two possibilities:

- if you have 6 (or more) trade than you need for your tech card you can buy another one simultaneously

or

- if you have at least 6 coins you can spend 6 trade, after buying the other card, to buy a new one

??

I think I don't understand the purpose of this wonder =(

thx!

It's the first case, when you have 6(or more) trade than necessary for your research, you can get extra technology