The HP-55 was a programmable handheld calculator; a lower-cost alternative to the

HP-65 The HP-65 is the first magnetic card-programmable handheld calculator. Introduced by Hewlett-Packard in 1974 at an MSRP of $795 (), it featured nine storage registers and room for 100 keystroke instructions. It also included a magnetic card re ...

. Introduced by

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...

in 1975, it featured twenty storage registers and room for 49 keystroke instructions. Its outward appearance was similar to the HP-65, but its silver band went through between the display and the keyboard like

HP-45 The HP-45 is the second scientific pocket calculator introduced by Hewlett-Packard, adding to the features of the HP-35. It was introduced in 1973 with an MSRP of US$395 (). Especially noteworthy was its pioneering addition of a shift key that ga ...

, its some key functions were different from HP-65 and it did not have a magnetic card reader/writer. Like all Hewlett-Packard calculators of the era and most since, the HP-55 used

Reverse Polish Notation Reverse Polish notation (RPN), also known as reverse Łukasiewicz notation, Polish postfix notation or simply postfix notation, is a mathematical notation in which operators ''follow'' their operands, in contrast to Polish notation (PN), in whi ...

(RPN) and a four-level automatic operand

stack Stack may refer to: Places * Stack Island, an island game reserve in Bass Strait, south-eastern Australia, in Tasmania’s Hunter Island Group * Blue Stack Mountains, in Co. Donegal, Ireland People * Stack (surname) (including a list of people ...

. Another feature of the HP-55 was that it officially featured a stop-watch function much similar to the hidden stop-watch function of the earlier

calculator. This stop-watch function could be accessed by setting the mode-slider to the Timer position. A quartz-crystal inside the calculator provided an accurate timebase, and it was advertised that the timer ran with as little as +/- 0.01% error. The data format used by the stop-watch consisted of a combination of units (Hours, Minutes and Seconds), but the HP-55 featured a special conversion function to convert between this format and a pure unit (Hours). Because of this, data from the stop-watch could easily be used right away in calculations. The HP-55 also featured several other conversion functions to instantly convert data between the

Imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texa ...

and

Metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathema ...

systems.

Bill Hewlett William Redington Hewlett ( ; May 20, 1913 – January 12, 2001) was an American engineer and the co-founder, with David Packard, of the Hewlett-Packard Company (HP). Early life and education Hewlett was born in Ann Arbor, Michigan, where his ...

's design requirement was that the calculator should fit in his shirt pocket. That is one reason for the tapered depth of the calculator. The documentation for the programs in the calculator is very complete, including algorithms for hundreds of applications, including the solutions of differential equations, stock price estimation, statistics, and so forth.

External links

The HP-55
at an unofficial Hewlett-Packard museum
MyCalcDB
.
1975 HP Calculator Christmas Guide

page at the unofficial Museum of HP Calculators {{HP calculators 55 Computer-related introductions in 1975

See also

External links