Chances of this?

Do I understand correctly that the chance to have a gem increase in level when vaaling it is 1/8 or about 12.5%?
So by vaaling 20 gems in a row and not getting the orb to increase is .875 x .875 to the power of 20? Is that correct? If so, then the chances of that occuring would be around 7% (so not astronomically low but fairly bad luck)?
I'm not great at math, I#d like to understand this better.
thanks in advance