The Day Runner PRO System Calculator/Ruler #492-113 is a versatile tool designed for business and office use. With solar power capabilities, this calculator/ruler is convenient and efficient for on-the-go calculations. Fits most 3 & 7 Ring Organizers make it easy to fit most planner and organizer systems, ensuring seamless integration into your existing setup. The Day Runner brand is known for quality and reliability, making this product a practical choice for those looking to streamline their office supplies.