if you don`t really want to get rid of your old calculator here is a usable way to keep it.
solar calculator (preferably old all you need from it is the circuit board and solar panel)
the place the red wire in side of one hole about a third of the way up the wire and twist the excess around the wire do the same with the other wire
when you finish that you`ll need to wrap the wires around each other to get it closer to the circuit board
take your decorations and use an adhesive to make them stick to the back of the circuit board