Hewlett Packard HP-35 Calculator (1972-1975)

✅ Hewlett Packard HP-35 

🥇First Handheld Scientific Calculator 

The Hewlett-Packard HP-35, launched in February 1972 for $395 (roughly $3,000 today), was the legendary "slide rule killer" that fundamentally changed science and engineering. As the world's first handheld scientific calculator, it was famously designed to meet a personal challenge from company co-founder Bill Hewlett: shrinking a 40-pound desktop computer into a device that could fit inside his shirt pocket. The HP-35 introduced the public to Reverse Polish Notation (RPN), a mathematical logic system that allowed users to input complex equations without ever needing parentheses, and it was the first pocket device capable of calculating advanced functions like sines and logarithms with a single keystroke. Its 15-digit bright red LED display and high-quality keys became the industry gold standard, and its extreme precision even allowed it to become the first scientific calculator used in space by astronauts on Skylab.

Source: eBay.com