Rocketbook Core Smart Notebook, Medium/College Rule, Gray Cover, (16) 11 x 8.5 Sheets - Provides a classic pen and paper experience, yet is built for the digital age. Although it feels like a traditional notebook, the Rocketbook Core is endlessly reusable and connected to all of your favorite Cloud services. When you write using any pen from the Pilot Frixion line, your writing sticks to Rocketbook Core pages like regular paper. But add a drop of water and the notebook erases like magic.