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HP 15C Programming Basics by Logan West

The HP-15C:

A Problem Solver

The HP-15C Advanced Programmable Scientific Calculator is a powerful problem solver, convenient to carry and easy to hold. Its continuous memory retains data and program instructions indefinitely until you choose to reset it. Though sophisticated, it requires no prior programming experience or knowledge of programming languages to use it.

The new HP-15C is a modern re-release of the original HP-15C introduced in 1982. While the battery life of the new version is now estimated to be 1 year for normal use, the calculator is now at least 150 times faster than the original. The low-power indicator gives you plenty of warning before the calculator stops functioning.

The HP-15C also conserves power by automatically shutting its display off if it is left inactive for a few minutes. But don’t worry about losing data – any information contained in the HP-15C is saved by Continuous Memory.

A Quick Look at v

Your Hewlett-Packard calculator uses a unique operating logic, represented by the v key, that differs from the logic in most other calculators. You will find that using v makes nested and complicated calculations easier and faster to work out. Let’s get acquainted with how this works.

For example, let’s look at the arithmetic functions. First we have to get the numbers into the machine. Is your calculator on? If not, press =. Is the display cleared? To display all zeros, you can press | ` that is, press |, then −.* To perform arithmetic, key in the first number, press v to separate the first number from the second, then key in the second number and press +, -, * or ÷. The result appears immediately after you press any numerical function key.

  1. If you have not used an HP calculator before, you will notice that most keys have three labels. To use the primary function – the one printed in white on top of the key – just press that key. For those printed in gold or blue, press the gold ´ key or the blue | key first.


The HP-15C: A Problem Solver 13

The display format used in this handbook is • 4 (the decimal point is ―fixed‖ to show four decimal places) unless otherwise mentioned. If your calculator does not show four decimal places, you may want to press ´• 4 to match the displays in the examples.

Manual Solutions

Run through the following two-number calculations. It is not necessary to clear the calculator between problems. If you enter a digit incorrectly, press

  1. to undo the mistake, then key in the correct number.

Notice that in the four examples:

  1. Both numbers are in the calculator before you press the function key.
  1. v is used only to separate two numbers that are keyed in one after the other.
  1. Pressing a numeric function key, in this case – * ÷ or Y, executes the function immediately and displays the result.

To see the close relationship between manual and programmed problem solving, let’s first calculate the solution to a problem manually, that is, from the keyboard. Then we’ll use a program to calculate the solution to the same problem with different data.

14 The HP-15C: A Problem Solver

The time an object takes to fall to the ground (ignoring air friction) is given by the formula


t = ,
HP 15c User Manual 1

where  t = time in seconds, h = height in meters,
HP 15c User Manual 3

g = the acceleration due to gravity, 9.8 m/s2.

Example: Compute the time taken by a stone falling from the top of the Eiffel Tower (300.51 meters high) to the earth.

300.51 v300.5100Enter h.
2 *601.0200Calculates 2h.
9.8 ÷61.3286(2h) /g.
¤7.8313Falling time, seconds.

Programmed Solutions

Suppose you wanted to calculate falling times from various heights. The easiest way is to write a program to cover all the constant parts of a calculation and provide for entry of variable data.

Writing the Program. The program is similar to the keystroke sequence you used above. A label is useful to define the beginning of a program, and a return is useful to mark the end of a program. Also, the program must accommodate the entry of new data.

Loading the Program. You can load a program for the above problem by pressing the following keys in sequence. (The display shows information which you can ignore for now, though it will be useful later.)

The HP-15C: A Problem Solver 15

Keystrokes Display


  1. CLEAR M 000-

HP 15c User Manual 5

Sets HP-15C to Program mode. (PRGM annunciator on.)

Clears program memory. (This step is optional here.)

Label “A” defines the beginning of the program.

The same keys you pressed to solve the problem manually.

―Return‖ defines the end of the program.

Switches to Run mode. (No PRGM annunciator.)

Running the Program. Enter the following information to run the program.

300.51300.51Height of the Eiffel Tower.
´A7.8313Falling time you calculated
1050 ´A14.6385The time (seconds) for a stone
to reach the ground after release
from a blimp 1050 m high.

16 The HP-15C: A Problem Solver

With this program loaded, you can quickly calculate the time of descent of an object from different heights. Simply key in the height and press ´A. Find the time of descent for objects released from heights of 100 m, 2 m, 275 m, and 2,000 m.

The answers are: 4.5175 s; 0.6389 s; 7.4915 s; and 20.2031 s.

That program was relatively easy. You will see many more aspects and details of programming in part II. For now, turn the page to take an in-depth look at some of the calculator’s important operating basics.

Part l



Section 1

Getting Started

Power On and Off

The = key turns the HP-15C on and off.* To conserve power, the calculator automatically turns itself off after a few minutes of inactivity.

Keyboard Operation

Primary and Alternate Functions

Most keys on your HP-15C perform one primary and two alternate, shifted functions. The primary function of any key is indicated by the character(s) on the face of the key. The alternate functions are indicated by the gold characters printed above the key and the blue characters printed on the lower face of the key.

  1. To select the primary function printed on the face of a key, press only that key. For example: ÷.
  1. To select the alternate function printed in gold or blue, press the like-colored prefix key (´ or |) followed by the function key. For example: ´ _; | £.

HP 15c User Manual 7

Throughout this handbook, we will observe certain conventions in referring to alternate functions. References to the function itself will appear as just the key name in a box, such as ―the W function.‖ References to the use of the key will include the prefix key, such as ―press | W.‖ References to the four gold functions printed under the bracket labeled ―CLEAR‖ will be preceded by the word ―CLEAR‖, such as “the CLEAR Q function,‖ or ―press ´ CLEAR M.‖

  1. Note that the = key is lower than the other keys to help prevent its being pressed inadvertently.


Notice that when you press the ´ or | prefix key, an f or g annunciator appears and remains in the display until a function key is pressed to complete the sequence.

HP 15c User Manual 9


Prefix Keys

A prefix key is any key which must precede another key to complete the key sequence for a function. Certain functions require two parts: a prefix key and a digit or other key. For your reference, the prefix keys are:

  • ^ • G f > i O m ´ | P I l F T s ? t H b < _ X

If you make a mistake while keying in a prefix for a function, press ´ CLEAR u to cancel the error. The CLEAR u key is also used to show the mantissa of a displayed number, so all 10 digits of the number in the display will appear for a moment after the u key is pressed.

Changing Signs

Pressing “ (change sign) will change the sign (positive or negative) of any displayed number. To key in a negative number, press “ after its digits have been keyed in.

Keying in Exponents

  • (enter exponent) is used when keying in a number with an exponent. First key in the mantissa, then press ‛ and key in the exponent.

For a negative exponent press “ after keying in the exponent.* For example, to key in Planck’s constant (6.6262×10-34 Joule-seconds) and multiply it by 50:

  • “ may also be pressed after ‛ and before the exponent, with the same result (unlike the mantissa, where digit entry must precede “).

20 Section 1: Getting Started


6.6262   -34

  • 6.6262   -34

50 * 3.3131 -32

The 00 prompts you to key in the exponent.




Enters number.


Note: Decimal digits from the mantissa that spill into the exponent field will disappear from the display when you press ―, but will be retained internally.

To prevent a misleading display pattern, ‛ will not operate with a number having more than seven digits to the left of the radix mark (decimal point), nor with a mantissa smaller than 0.000001. To key in such a number, use a form having a greater exponent value (whether positive or negative). For example, 123456789.8×1023 can be keyed in as 1234567.898×1025; 0.00000025×10-15 can be keyed in as 2.5×10-22.

The “CLEAR” Keys

Clearing means to replace a number with zero. The clearing operations in the HP-15C are (the table is continued on the next page):

Clearing SequenceEffect
|`Clears display (X-register).
In Run mode:Clears last digit or entire display.
In Program mode:Deletes current instruction.
´CLEAR ∑Clears statistics storage registers, display,
and the memory stack (described in
section 3).

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