In 1972, the Hewlett-Packard company (commonly known as HP) introduced the first ever scientific pocket calculator, called the HP-35. The term scientific meant that it was able to calculate trigonometric and exponential functions. The HP-35 was the first ever calculator to do these calculations; prior calculators only performed addition, subtraction, multiplication and division.
Before the introduction of the HP-35, trigonometric and exponential calculations were done using a slide rule, which were only accurate to a few significant figures. The fact that you may have never even heard of or seen a slide rule before is because the introduction of this calculator made slide rules obsolete.
|An HP-35 Scientific Pocket Calculator|
Image Credit: Seth Morabito
The name HP-35 came from the 35 keys on the device. It was only anticipated to sell about 10,000 units in the first year. However, HP greatly underestimated the demand for such a device and ended up selling over 100,000 in the first year.