Calculator - 1980-1990 - HP 28S

Iconic highly advanced programmable scientific calculator Hewlett-Packard HP 28S, a true piece of history of computing and pocket calculation. Introduced to the market in 1988 as the evolution of the 28C model, the 'S' version stands out for its upgraded RAM of a full 32 KB and a faster custom Saturn microprocessor at 1 MHz.

This model is famous among collectors and enthusiasts for its revolutionary book-style (clamshell) design with a dual input interface: on the left a full alphabetic keyboard and a handy quick reference guide for the syntax of objects, while on the right sits the numeric keypad integrated with the main calculation controls. It was one of the earliest graphical calculators capable of performing mathematical and algebraic operations purely symbolically, introducing the innovative RPL programming language based on Reverse Polish Notation (RPN). The calculator presents itself in excellent cosmetic condition, with legible inscriptions and silkscreens and well-preserved plastics.

Excellent mechanical and electronic condition. The device is fully functional and has been successfully tested: it passed both HP's native diagnostic test for key integrity and responsiveness, and the LCD pixel test (as shown in the photo gallery). Aesthetically, the outer plastic case shows some light signs and superficial scratches due to age and use, while the internal silkscreens and keyboards are well preserved and sharp.

Accessories: Includes the original paper user manuals from the period. The original box is not present. Also included are 4 N-type (1.5V) batteries.