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
Another pocket-sized scientific achievement: The HP-21. $125*
We designed it for what we believe to be a growing class of calculator-oriented
people who appreciate the very high quality that we put into HP pocket
calculators but who don't require all the features and functions of our HP-45,
55, and 65.
The HP-21 is more compact than our other pocket-sized calculators. Closer
to palm size. The minute you've grasped its keyboard's elegant simplicity,
you'll see that it has considerably more capability than our pace-setting
HP-35, presented in an easily comprehensible way.
An addressable storage register with four-rule arithmetic in and out.
Rectangular-to-polar conversion and vice versa.
Choice of floating-point or scientific notation, and control over the number
of places displayed. When numbers get too large or too small for the
floating-point, the display automatically switches to scientific.
Single-keystroke calculation of a common antilog (10x).
In addition, the HP-21 gives you
Keys for all the basic trigonometric functions (sin, cos, tan,
sin-1, cos-1, tan-1).
Keys for ex yx Ln, Log, sqrt(x), 1/x, x<>y, PI.
A 10-digit display and 2-digit exponent.
Rounding to last displayed digit.
Error displayed if you key in an impossible instruction.
The HP logic system and four-register stack that save you keystrokes, show
you all intermediate results, let you proceed naturally through the most
complicated expressions without restructuring or keeping track of parentheses,
and let you backtrack to correct errors.
Function keys where you can see them without moving your hand (unless you're
Execution of any function in less than one second.
In keeping the price down, we haven't skimped traditional HP quality details,
some of which you can see and feel, many of which are hidden.
Double-injected keys. The legends go all the way through and will never wear
Positive click on each key so you'll feel the connection.
Moisture barrier under the keyboard to protect against spills.
Single-unit battery pack that can only be inserted the right way, plus recharger.
Gold-plated internal connections.
Recessed display for better visibility outdoors.
Rugged case with rounded edges. Withstands most tumbles to the floor.
Soft vinyl zippered carrying pouch.
You will find the HP-21 at leading department stores and college book stores
throughout the United States, along with our other hand-held models for science
and business. For the name of your nearest dealer, write to Hewlett-Packard,
call toll-free, (800) 538-7922 (in California it's (800) 662-9862).
*Domestic USA prices only.
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