The Museum of HP Calculators

This Hewlett-Packard advertisement, originally published in Scientific American, is used by permission. If errors crept in during the scanning process, please contact Dave Hicks

The HP Professionals-the calculators with the specialized capabilities you need-have a new member: the HP-91. It's scientific, it's portable, and it prints.

Our first battery-operated portable printing calculator, the HP-91 weighs only 2 1/2 pounds (1.13 kg) and fits in your briefcase with plenty of room to spare. Like all the other HP Professionals, it uses HP's logic system with a four-register stack and a unique key that opens the door to answers you can trust. In addition, it gives you a complete printed record of your scientific calculations, whether you use it on battery power or line current.

The HP-91 Scientific Printing Calculator retains the convenience of a hand-held calculator while providing a "hard copy" record from a quiet thermal printer. So small and light that you can easily carry it in a briefcase, it operates on its own batteries for as long as seven hours before they need recharging.

Its comfortably large LED display shows up to 10 significant digits, plus a two-digit exponent and appropriate signs. While the HP-91's display shows all keyed numbers and answers, its printer operates in any of three modes: one provides a complete record of your calculations-all entered data, all functions, and all intermediate and final answers; the second records only entered data and functions; in the third, the printer operates only on keyed command.

The HP-91's buffered keyboard lets you enter data as fast as your fingers can press the keys-up to seven characters ahead of the printer--while the printer records the calculations at its own pace.

In terms of calculating power, the HP-91 provides a full range of functions for scientists and engineers. Its math capabilities include log; trig in degrees, radians, or grads; rectangular/polar conversions; and three separate percent functions. Its statistics capabilities include summations, two-variable mean and standard deviation, linear regression, linear estimates, and factorial.

The HP-91 also has 16 addressable memory registers, with register arithmetic capability in 10 of them; a "Last-X" register for easy error recovery; four convenient clearing operations; and a choice of display and printing in fixed decimal, scientific notation, or engineering notation (values with exponents that are multiples of three).

Price is $500* for the calculator with battery pack, recharger/AC adapter, case, 220-page applications and instruction handbook, and two rolls of thermal paper for the printer. Try the HP-91 at selected local retailers. You'll find it a new and recording experience.

Call 800-538-7922 in the U.S.A. (in California, 800-662-9862) for detailed information and the name of the HP retailer nearest you.

*Domestic USA prices only.

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