At HP-25.
The HP-25 was a scientific and engineering programmable hand-held calculator made by Hewlett-Packard between 1975 and 1978. The HP 25 was introduced as an inexpensive alternative ($ 195 MSRP) of the new HP 65. .
To reduce costs, the HP 25 omitted the HP 65's magnetic card reader, so it had to be programmed using the keyboard. After shutting down, the program was lost and, if needed again, had to be typed again. The HP 25C, introduced in 1976, solved this defect with the use of battery-backed CMOS memory, called HP continuous memory. Description
Like all early HP calculators, the HP 25 used Reverse Polish Notation (RPN) for calculations, working with a stack of four levels (x, y, z, t) as temporary calculation records. Almost all the buttons had two alternate functions, which were accessed by the use of a blue prefix key and a yellow one. With a small sliding switch you could switch between the run mode and the program mode. The HP 25 had a 10-digit red LED display and was the first calculator to enter the "engineering" display option, a mantissa / exponent format where the exponent is always a multiple of 3 to match the common prefixes of the YES, such as mega, kilo, mili, micro, nano.
The HP 25 had memory for up to 49 program steps. It was the first HP calculator to use fully combined key codes (storing prefix key and function key together in a program position) to save memory space. In addition, there were 7 storage records and scientific functions and specialized statistics. The owner's manual came with 161 pages in four colors and contained many examples of mathematical, scientific, navigation and financial programming. Notes
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