9100A Desktop Calculator, 1968
Really a desktop computer, the 9100A combined Reverse Polish Notation (RPN) — a system for representing mathematical expressions without the use of parentheses — with a special algorithm that could handle trigonometric and logarithmic functions. HP sold the 9100A as a calculator because at the time the perception was that a computer had to be big to be credible. Bill Hewlett said "If we had called it a computer, it would have been rejected by our customers' computer gurus because it didn't look like an IBM. We, therefore, decided to call it a calculator and all such nonsense disappeared."
The 9100A is now recognized throughout the industry as the first desktop computer. In December 2000, Wired Magazine named it the first personal computer.
The 9100A is the world’s first programmable scientific desktop calculator.