The HP-41C series are programmable, expandable, continuous memory handheld RPN calculators made by Hewlett-Packard from 1979 to 1990. The original model, HP-41C, was the first of its kind to offer alphanumeric display capabilities. Later came the HP-41CV and HP-41CX, offering more memory and functionality.
Read more about HP-41C: The Alphanumeric "revolution", Expandability, The HP-41CV and CX, Programming, The HP-41C Community and Synthetic Programming, Smithsonian Museum