this is interestin as for scrolls i have to say that:

-A 100% scroll will always work
-A 60% scroll may work 6 times out of 10.
-A 10% scroll may work only 1 time out of 10.

you get it since may stands for maybe and that means its random again and another Dice with 1000 sides rolls and determinates by the chance of the scroll procentage wich Scroll will work.

all in all

Nice Guide d O.o b