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{{Use dmy dates|date=April 2019|cs1-dates=y}}
{{Infobox Calculator
| name    = HP-25
| image   = HP-25-front.jpg
| display_size = 10-digit red LED
| entry        = [[Calculator input methods#RPN|RPN]]
}}

The '''HP-25''' was a hand-held [[programmable calculator|programmable]] [[scientific calculator|scientific]]/engineering calculator made by [[Hewlett-Packard]] between early January 1975 and 1978.  The HP-25 was introduced as a cheaper ([[US$]]195{{ref|price}} MSRP) alternative to the ground-breaking [[HP-67]]. Similar to the way the HP-55 was a cheaper alternative to the HP-65.

To reduce cost, the HP-25 omitted the HP-67's [[magnetic card]] reader, so it could only be programmed using the keyboard. After switching off, the program was lost and had to be typed in again. The model HP-25C, introduced in 1976, addressed that shortcoming through the first use of battery-backed [[CMOS]] memory in a calculator, termed ''[[HP Continuous memory|continuous memory]]'' by HP.

Like all early HP calculators, the 25 used the [[Reverse Polish Notation]] (RPN) for entering calculations, working on a four-level [[Stack (abstract data type)|stack]] (x,y,z,t). Nearly all buttons had two alternative functions, accessed by a blue and yellow prefix key. A small sliding switch was used to change between "run" and "program" mode. The HP-25 used a 10-digit red [[LED]] display and was the first calculator to introduce the [[engineering notation|"engineering" display option]], a denormalized mantissa/exponent format where the exponent is always a multiple of 3 to match the common [[SI|SI prefixes]], e.g. mega, kilo, milli, micro, nano.

The HP-25 had memory space for up to 49 program steps. It was the first HP calculator which used fully merged keycodes (storing prefix key and function key together in one program location) to save memory space. Additionally there were eight storage registers and specialized scientific and statistical functions. The owner's manual came with 161 pages in four colors and contained many mathematical, scientific, navigational and financial programming examples.

The HP-25 was about 25% smaller than the HP-65. It used the same trapezoid profiled keys introduced with the HP-65. The HP-25 was regarded as a competitor to the [[TI-58]] and TI-58C calculators offered by Texas Instruments. Looking strictly at the functionality and capacity, the more equal competitor would be the [[TI-57]]. It lacked a few of the HP-25's functions, but had some other advantages.

One notable deficiency of the HP-25/25C was the lack of a subroutine capability, at a time when the TI-58 and even the earlier SR-56 had subroutines. Although 49 [[fully merged keycodes]] were roughly equivalent to the unmerged 100 steps of the SR-56; by the time the TI-58 arrived with 480 steps, subroutines, DSZ loops, etc., the HP-25/25C had serious competition. HP went on to introduce the HP-29C/19C calculators with 99 merged steps, labels, and subroutines. And TI introduced a TI-58C with continuous memory.

{{anchor|25 GD}}A version adapted to support an additional backward-facing display manufactured by Educational Calculator Devices named EduCALC 25&nbsp;GD existed as well.<ref>{{cite magazine |title=The EduCALC |magazine=[[65 Notes]] |date=February–March 1976 |volume=3 |number=2 |page=8 |url=https://www.hpcalc.org/hp48/docs/columns/edu-calc.html |access-date=2022-07-01 |url-status=live |archive-url=https://web.archive.org/web/20170704064503/http://www.hpcalc.org/hp48/docs/columns/edu-calc.html |archive-date=2017-07-04 |via=HP Museum}}</ref>

== See also ==
* [[HP calculators]]
* [[List of Hewlett-Packard products#Pocket calculators|List of Hewlett-Packard products: Pocket calculators]]

== Notes ==
# {{note|price}} [[US$]]195 in 1975 ≈ [[US$]]770 in 2009  (see [https://web.archive.org/web/20110718031608/http://www.westegg.com/inflation/ The Inflation Calculator])

== References ==
{{reflist}}

== External links ==
* [http://www.hpmuseum.org/hp25.htm The Museum of HP Calculators' article on the HP-25]
* [https://archive.computerhistory.org/resources/text/HP/HP.PocketCalc.1975.102646259.pdf 1975 HP Calculator Christmas Guide]
* [http://mycalcdb.free.fr/main.php?l=0&id=779 HP-25] and [http://mycalcdb.free.fr/main.php?l=0&id=783 HP-25C] pictures on [http://mycalcdb.free.fr MyCalcDB] (database about 1970s and 1980s pocket calculators)
* [https://web.archive.org/web/20120314032418/http://www.jacques-laporte.org/Woodstock/ws_HW_main.htm HP-25 hardware details]
* [http://www.pahhc.org/2007/HHC2007/HP_brochures/hp25.pdf HP-25 Brochure from Hewlett-Packard]
* [http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1975-11.pdf Hewlett-Packard Journal, November 1975] {{Webarchive|url=https://web.archive.org/web/20120520114546/http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1975-11.pdf |date=2012-05-20  }}

{{HP calculators}}
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[[Category:HP programmable calculators|25]]