HP-22S

The HP-22S was a scientific calculator produced by Hewlett-Packard from 1988 to 1998. It was designed primarily for students and engineers and offered a combination of algebraic and RPN (Reverse Polish Notation) entry modes.

Notable features of the HP-22S included its fraction mode, allowing calculations to be performed and displayed using fractions, and its ability to handle complex numbers. The calculator also had statistical functions, including standard deviation and linear regression, as well as trigonometric and logarithmic functions. Its matrix operations were relatively basic compared to later models, but still provided functionality for solving linear equations and performing matrix arithmetic.

The HP-22S used a two-line LCD display. The top line displayed the entry, while the bottom line displayed the result. This facilitated error checking and made it easier to follow calculations. The calculator was powered by button cell batteries.

Although discontinued, the HP-22S remains a popular choice among users who prefer its combination of functionality and ease of use, particularly its fraction and RPN capabilities. It is considered a reliable and versatile calculator for general-purpose scientific and engineering calculations.