HP-25

The HP-25 was a hand-held programmable scientific/engineering calculator made by Hewlett-Packard between 1975 and 1978. The HP-25 was introduced as a cheaper (US$195ref|price MSRP) alternative to the ground-breaking HP-65.

To reduce cost, the HP-25 omitted the HP-65's magnetic card reader, so it had to 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 use of battery-buffered CMOS memory, termed 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 (x,y,z,t). Nearly all buttons had two alternate 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" display option, a denormalized mantissa/exponent format where the exponent is always a multiple of 3 to match the common 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 7 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.

External links

* [http://www.hpmuseum.org/hp25.htm The Museum of HP Calculators' article on the HP-25]
* [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 70's and 80's pocket calculators)

Notes

# US$195 in 1975 ≈ US$710 in 2005 (see [http://oregonstate.edu/Dept/pol_sci/fac/sahr/sahr.htm Inflation Conversion Factors for Dollars] )