The History of HP Calculators

Hewlett-Packard started making calculators in the late 1960’s. Given the company’s knowledge on technology, they saw an opportunity to replace slide rules and adding machines. With this goal in mind, they invented a desktop scientific calculator that included powerful capabilities that handled trigonometric functions, exponentiation, square roots, logarithms and floating-point numbers. The HP scientific calculator’s success became the start of a series of calculators with varying capabilities from the company.

Here is a brief history of HP calculators that changed the way people compute for complex equations.

HP 9100 (1968)

This is the first HP scientific calculator and it was introduced in 1968. It was made with a printed circuit board ROM, magnetic core memory, a CRT display, and weighed around 40 pounds. This calculator performed different functions like logarithmic, square root, trigonometric, vector addition/subtraction, polar/rectangular conversion, floating-point numbers and a logic system that handles complex expressions (RPN). It also had a magnetic card reader/writer and options to print or plot.

There are two versions of this model, the HP 9100A and HP 9100B. Shortly after the HP 9100A’s release, the HP 9100B came out with added features like a maximum of 32 storage registers and 392 program step (the 9100A had maximums of 16 storage registers and 196 programs steps). The HP 9100B also had a dual program display, a key to recall numbered registers into X, and subroutines.

HP’s entry product to the electronic calculator market performs beyond simple computations and its success convinced Bill Hewlett to create something of the same power but costs less, weighs less, and something that can fit into a pocket.

HP-35 (1972)

The realization of Bill Hewlett’s vision to create a pocket-sized calculator is the HP-35. It was introduced in 1972 as the first pocket handheld calculator that performed more than the four basic functions. This is the first handheld HP calculator that performed trigonometric and logarithmic functions with a keystroke, and was known for having the x^y key instead of the y^x. It was originally developed for internal use to make engineers’ jobs easier before they introduced it to the market and sold hundreds of thousands.

HP-80 (1973)

This is the second handheld calculator and the first HP business calculator. Introduced in 1973, it was designed to solve problems that did not require the users to know the formulas, ideal for finance rather than scientific/engineering functions. Compared to the HP-35, the users supplied the formulas on the HP- 35 whereas the HP-80 supplied the formulas for the users. This calculator had date arithmetic, bond and depreciation calculations, statistic functions, and control of the display mode. It was the first calculator from HP to have a shift key and it added 11 other functions in this model. The x^y functions of the HP-35 were replaced with y^x and had the STO and RCL buttons to allow users to store and recall numbers to and from registers.  Except for their functions, the HP-35 and HP-80 are similar in construction, batteries, and dimensions.

HP-65 (1974)

This was introduced in 1974 as the fourth handheld calculator and first pocket programmable model from HP. It had new functions for programming and had a built-in device for reading and writing magnetic cards so that users can save programs on cards. It was dubbed as “The Personal Computer” and it used label addressing and had 100 lines of space. It was the first HP pocket calculator with base conversions (octal and decimal), and the first to perform degress.minutes seconds arithmetic.

HP-27 (1976)

This was HP’s first “Do Everything” pocket calculator because it performed different functions for math, statistics, scientific, and business. In addition to the usual statistical functions, this model added computation of variance and normal distribution parameters. It was ideal for business users who needed technical functions and for technical users who needed business functions, without the need for programmability.

Within just a decade of entering the electronic calculator market, HP already made a number of calculators for different computing needs. HP calculators evolved from basic computing to scientific/technical and financial/business computing. Today, HP continues to provide us with calculators to help us with our daily computing needs.


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