This step is very easy. I take the card and set it on the device and mark out where the slots on the device are. I align one of the sides of the card to one side of the opening to make for less cutting and a higher level of accuracy. I make sure of my measurements after I make my marks by putting the card back up to the battery compartment and giving it a twice over.
Please see pictures and hover over picture Squbbles (Square Bubbles)!!!