We will need:

• eraser
• a blank A4 sheet, preferably quite stiff
• scissors
• a knife
• tape
• line

How to do it?

First of all, we have to measure the eraser (Note: to make this cheat sheet, the best is a regular, cubic eraser, without any quirks in the shape and one that is not noticeable! Moreover, it is very good if it is new, i.e. not rubbed and clean. it will be perfectly white, the paper stuck to it will not be conspicuous.), check all its dimensions, and then cut such a strip to cover the entire elastic band, except for its smallest sides.
Use a knife to make a slot in the upper part of the largest wall of the elastic band, into which we put the previously prepared belt with the elastic band and wrap it around the elastic. When the teacher cannot see, we develop a cheat sheet and rewrite it. Attention! It is important that the sheet is not written on one surface of the rubber band, then the band will be invisible.