The HP-21 is a full-function scientific pocket calculator that offers features and functions not available on apparently similar models. Most important of these is HP’s remarkably efficient RPN logic system which gives you the problem-solving power of an ’equals’ key and at least three levels of parentheses. Yet, this ingenious system is distinguished by its similarity to your natural way of solving mathematical problems. It allows you to approach the solution of every problem in the same natural manner as you would with a slide-rule, through the process of equation simplification. Since there is no need to reformat equations to fit machine logic, operation is easy. And it is made even easier by the fact that you only work with one or two numbers at a time. When you press any function key. it executes the function immediately and you see every intermediate answer. This allows you to check your progress every step of the way through even the most complex equations. The four-register operational stack actually handles the detail work for you automatically, saving up to four intermediate solutions for further operations.

Other features of the HP-21 include:

Rectangular/polar coordinate conversions

The HP-21 converts rectangular coordinates to polar coordinates (and vice versa) easily, thus simplifying vector addition and subtraction.

Display format selectivity

Choose between scientific notation and fixed decimal display formats. With the fixed-decimal format, you select how many decimal places you wish to see (up to 9). In scientific notation, you can select up to 8 significant digits in the mantissa. Although the HP-21 provides you with automatic round-off to the selected decimal place, 10 significant digits are retained internally and used for all computations.

Full register arithmetic

In addition to its four-register operational stack, the HP-21 provides a separate addressable memory for storing constants or other data. And you can perform all four arithmetic operations directly upon this stored data. And, of course, not having to recall and store data to pc-form an arithmetic operation makes your calculation just that muck simpler.

Degree/radian mode selection and conversion capability

The H P-21 lets you express angles in either degrees or radians. at_ perform trig operations in either angular mode. It also simplifies co–version from one angle mode to the other.

In short, the HP-2l gives you all the functions/features you need to solve real-world scientific or engineering problems. And, its solid design and construction continue the HP reputation for quality products.

HP-21 Specifications

Pre-programmed functions

Trigonometric (all in degrees or radians): Sin x: Arc Sin x: Cos x: kit Cos x: Tan x: Arc Tan x.

Logarithmic: Log x. Ln x: ex: 10x.

Other: yx; 1/x: ir: rectangular/polar coordinate conversion: fui register arithmetic.


Memory: one addressable register: four-register operational stack. Display: up to 10 significant digits in fixed-decimal notation: up to significant digits plus two-digit exponent in scientific notation: full display formatting in either mode with selective round-off indicators for improper operations. low battery.

Dynamic range: 10-19 to 1019 (200 decades).

Power: AC: 113 or 230 V. ± 10c. 50 to 60 Hz, 5 watts. Battery: 22-5 Vdc nickel-cadmium rechargeable battery pack.

Dimensions: length: 13.0 cm (5.1’). Width: 6.8 cm (2.7’). Height: 3-0 cm l (1.2’).

HP Measurement + Computation Catalogue 1976