The Evolution of the Calculator Keypad: From 9 Keys to the Standard 10

The layout of the calculator keypad wasn't always as we know it. Early Comptometers used a 9-key layout, driven by mechanical constraints (e.g., lever connections to rotating drums) and user experience considerations (placing frequently used keys within easy reach for efficiency). However, this design required highly trained users for optimal performance. The Dalton revolutionized this with a 10-key layout, including 0 for the first time, and a more compact design for improved usability. Finally, Sundstrand's 3x3 layout, with its ergonomic design, became the standard for calculator keypads, still used over 100 years later.