The disc calculator, also known as ready reckoner comes in a variety of sizes with 2 or 3 wheels that can have apertures to show information underneath. Eyeleted with a plastic or metal eyelet to make the disc spin as you push it round. Any branded information could be revealed, but examples are medical information like BMI or pill dosages, tax or investment calculators, sunscreen calculators, automotive or technical. Disc calculators are great promotional items as they are interacted with and kept as useful tools.
Example ideas/uses: Could be as part of a promotional pack, mailed out in an envelope or given away by sales reps on calls or at trade shows.