Ruling Question about a certain stadium card?

[the ultimate master]

On the stadium card, Lake Boundary, it says that the weakness becomes x2 instead. What does x2 mean? I'm only familiar with adding and subtracting damage?

 

[Wizzblade]

That damage is multiplied by the number 2.

 

[the ultimate master]

Can you show me an example, please?

 

[Po-Po-Pocchama]

Empoleon takes 20 damage from a Pikachu. Now normally it would be 50 (+30 Weakness) but instead it does 40 (Lake Boundary does 20 times 2 instead of +30) This could end up in less damage or even more.

 

[the ultimate master]

Thanks, now I get it!