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 in 2026 dollars), was the "slide rule killer" that fundamentally changed the engineering profession. As the world's first handheld scientific calculator, it was famously designed to meet Bill Hewlett’s personal challenge: shrinking the power of the 40-pound HP-9100A desktop computer into a device that could fit inside his shirt pocket. The HP-35 introduced the public to Reverse Polish Notation (RPN), a logic system that uses a four-level stack to evaluate complex expressions without parentheses, and it was the first pocket device capable of performing transcendental functions like sines, logs, and roots with a single keystroke. Its 15-digit red LED display and high-quality "double-shot" molded keys became the industry gold standard, while its precision allowed it to become the first scientific calculator used in space by astronauts on Skylab. Today, restorers often have to contend with the "alkaline plague" from old NiCd batteries and a known exponential bug in the earliest units (where 2.02 ln ex incorrectly yielded 2), making these unpatched first-run models prized artifacts of computational history.

Source: eBay.com