The first hand-held electronic calculator, nicknamed 'Cal-Tech,' was developed by a team at Texas Instruments led by Jack Kilby. Before this, calculators were the size of typewriters and required being plugged into a wall. The Cal-Tech used integrated circuits to perform addition, subtraction, multiplication, and division, and it printed results on a small strip of thermal paper. By the early 1970s, the introduction of LED and LCD screens made these devices even smaller and more affordable. The pocket calculator replaced the slide rule, which had been the standard tool for engineers and scientists for centuries. It democratized mathematics, allowing students and professionals to perform complex calculations quickly and accurately, and paved the way for the development of even more powerful portable computing devices.