HP Calculator History - The HP-91

by Wlodek Mier-Jedrzejowicz Ph.D.


Introduced on March 1 1976, this was the tenth small electronic calculator sold by HP - but the first one too big to be considered a "handheld". HP called it a "Scientific Portable Printing Calculator" to distinguish it from the smaller models and from their much bigger desktop models.

It introduced HP's third family of calculators after the original Classic family and the small Woodstock models, the Topcat family. It was not programmable, had 16 storage registers, a standard set of scientific and RPN functions, statistical functions, and of course the printing functions - print the X register, the stack, the statistics registers, and all registers. It had linear regression and H.MS arithmetic but no functions to convert between units. The printer was a thermal model - using temperature sensitive paper, more expensive than ordinary paper but saving the trouble of fiddling about to change a ribbon.

Since the HP-91 could not be called a "handheld calculator" the question arises whether it should be included in this series of articles about the history of handheld HP calculators - see the article "HP Calculator History - What Are We Talking About?". As befits a top cat, the HP-91 codename was "Felix".


This article is part of the WMJARTS file. This file contains a series of articles written by Wlodek Mier-Jedrzejowicz and published in DATAFILE, the journal of the HPCC. The article was reproduced with permission of the author.

Copyright Wlodek Mier-Jedrzejowicz Ph.D.