The interest rate doesn’t add up!

Hey there guys… congrats in this great plugin!
There’s only one problem that I’m having: the value of the interest rate doesn’t add up correctly mathematically speaking or maybe I’m missing the logic of the math behind this.
So if the value is “1” then the result should be: price x exchange rate x interest = final product price.
In my case I want to add 19% to the converted price and if I put 19 in the interest field I get a huge sum so I tried putting 1.19 because this is how you add 19% to something, you just multiply it with 1.19 but it still doesn’t show the correct result.
To get a similar result I had to put 0.9 in the interest field but that’s not accurate either.
So again, what is the logic behind the interest because I didn’t find anything on your documentation website about this.

Thanks in advance!