1.) Take the back cover off. All the screws are the same so don’t worry.
3.) Turn the calc over and hold it by the edges. Now take a damp cotton swab and gently press down on each key until the key is below the front cover. Wipe around the inside of the hole. Now let the key raise back up and wipe the sides of the key. Do this with the rest of the keys.
4.) Put the 2 screws on the back into the boards.
5.) Put the back cover back on. hook it over the USB port and 3-pin port, and then guide the battery springs into their slots.
6.) Put all the screws back in.