In one sentence, describe what the following article is about:

Loop a thick rubber band around a book and write on it while it's stretched out. Your writing will just look like a random design once it returns to its original size. Wait until no one is looking, then give the rubber band a tug and watch your notes magically appear. Make sure you write your letters nice and small. That way, no one will be able to tell what they are until you stretch out the rubber band. Remove the label from a bottle of water and scan it onto your computer. Open the file in an image editor and replace all the visible text with crib notes. Once you're done, print out the fake label and attach it to the bottle using a dab of glue. If you don't have a scanner or printer at your disposal, you can write on the inside of the label, then reattach it using a dab of glue. To make the most of the space you have, try to cover as much of the label as possible, including the areas where the product slogan, serving info, and ingredients list would usually go. Either scrawl the answers directly onto your desktop (if you have an assigned seat) or put them on a "blank" sheet of paper and keep it out during the test. They'll glow brightly when illuminated with UV keychain light, but will remain unseen to anyone passing by the rest of the time. You can buy invisible ink online or at most craft stores for around $10 a bottle. Another option is to shop around for a set of invisible ink pens. These often come with handy UV mini-flashlights built in. Sometime before your test, make a list of any items you don't understand and tag them on the wall of one of the stalls in the bathroom. If things go south during the exam, tell your teacher you urgently need to use the restroom and slip away to consult your secret treasure trove of knowledge. Leave your answers in out-of-the-way places where someone will be unlikely to spot and erase them. It's also a good idea to use pencil or washable marker to avoid getting in even more trouble if you happen to get busted.

Summary:
Turn a rubber band into a covert cheat sheet. Print your notes on a water bottle label. Write down the answers to the test in invisible ink. Graffiti a bathroom stall with test answers.