Doing Arithmetic Part II: Simple Hands-on Examples Using Five HP CALC Applications

By Hal Goldstein

Last issue (Sep/Oct 93) we began exploring HP CALC's Arithmetic application with some examples and explanations. Hopefully, we got some of you using HP CALC. In this issue we will continue to give you a flavor of the powerful, easy-to-use applications available from a press of the blue HP CALC key.

In this article we will use variations of one simple, common arithmetic problem to discover how to use some of HP CALC's different applications. The purpose of this exercise is to introduce you to some of the HP CALC applications that can be used every day by most people.


We enter a store that advertises that all items are 15% off the marked price. We want to know immediately the exact cost of a given item. Let's look at the different HP CALC applications in which we could solve that problem. At the same time we will look to see what kinds of problems the HP CALC application is ideally suited for.

How to Start an HP CALC Application on the Palmtops

The HP 100LX version of HP CALC has a few more applications and features than the 95LX version, but is otherwise the same calculator. To bring up the HP CALC applications on the 95LX, press (HPCALC) (MENU) and select any of the seven applications (Arith, TVM, Solve, Math, Bus%, List, or Conv) from the top row.

On the 100LX, start HP CALC and press (MENU) Applications. The pull down menu will list ten applications: TVM Cash Flows, Business%, Solver, List Stat, Conversions, Math, Custom, Date Calcs and Arithmetic. Simply choose the application you wish.


Let's open the Arithmetic application and use it to determine the discounted price.

Suppose the first price we encounter was $39.95. We could simply type 39.95-15% and press (ENTER). We would get the answer $33.96. HP CALC arithmetic conveniently and intuitively interprets 39.9515% as 39.95 minus 15% of 39.95.

Since all the sale items are 15% off, a better approach would be to make -15% a "constant". We do so by entering 39.95--15% (enter the minus sign twice). We come up with the same answer, $33.96, but the bottom right now lists the constant [-15.00%]. That means when we enter a number and press (ENTER), 15% will be subtracted from the number we entered.

(As discussed last issue we can create a constant simply by entering the operand (+, -, *, /, or ^) twice. So if we wish to square a bunch of numbers we could type 0^^2 and [^2.00] appears. Typing another number and pressing (ENTER) would square it).

Arithmetic provides a straight-forward way to determine sale price; however there are other methods.


The Business Percentage application was created to solve percentage problems (Bus% on the 95LX and Business% on the 100LX). Suppose the retail price of the next item we came across was $55.95. We enter HP CALC's Business% application and type 55.95 and press (F7) (TOTAL). Next we key in 85 and press (F9) (%TOTAL). (This stands for the percentage of the total. A 15% discount translates into 85% of the total). Finally, we press (F8) (PART) to find that the item will cost $47.56.

To continue determining sale prices, press down arrow to highlight Total amount ............ TOTAL. Key in the new item price, for example, 6.50. Press (F8) (PART) to discover your price of $5.53.

Bus% Screen in HP Calc:  Graphic

 While we are in the Business% module, let's take a quick look at the top three lines of the screen. Suppose at that sale store there was a special marked down rack. We saw an item, previously priced at $27.50 with a line through it followed by $19.95. What percentage discount would we be getting? Type 27.5 and press (F3) (OLD). Now type 19.95 and press (F4) (NEW). Finally press (F5) (%CHG). The percent change will be entered at the end of the third line. Since it's a markdown, it is a negative number, -27.45 (a 27.45% discount).

List Function

This application can be used to list a number of discounted items and calculate their sum.

Go to List on the 95LX and List Stat on the 100LX. If the 100LX displays 2-var within the horizontal line, press (F4) (1-Var). 1Var should appear on the horizontal line. Clear any leftover data from the List function by pressing (MENU) Erase Data on the 95LX and (MENU) Clear Data on the 100LX.

Suppose we find four items priced at $32, $15.95, $17, and $3.50. We would enter them into List by keying in 32-15% (ENTER), 15.9515% (ENTER), 17-15% (ENTER), and 3.50-15% (ENTER). The resultant screen would look like this, with the sum of $58.18 showing at the bottom.

List Stat Screen :  Graphic

 Unfortunately, List does not allow the use of constants like Arithmetic does, so entering 32--15% won't help. If you wish to use constants, or if you have a more complicated problem, you can create User Defined Function Keys (System Macros) that toggled you between Arithmetic and List. You can use the constant feature in Arithmetic to compute a result, which remains on the calc line when you switch to List. Pressing (ENTER) puts the result on the list.


Solver is one of the most powerful and useful HP CALC applications. It is especially useful for people in technical fields. Solver let's you write your own equations and have the HP Palmtop solve them. Even if you are not an engineer, you may find Solver useful. You could write equations for budgeting, figuring out taxes, determining gas mileage, and more. Ed Keefe illustrated on page 37 of the Mar/Apr 93 issue that you can even create an equation to select your Lotto numbers for you. Whatever your needs, Solver could be for you.

Our example is a relatively simple use of Solver. To compute our sale price we must multiply the percent discount times the retail price and then subtract that quantity from the retail price. On a $100 item we subtract 15% * $100 from $100 to get $85. If we were to write a generic algebraic equation for this using words for variables, it would look like this:


Go to the main Solver screen. On the 100LX press (F2) (Insert) and (F6) (Edit). On the 95LX press (F4) (Insert) and (F2) (Edit). Type in the above formula. Make sure you type in the word "ListPrice" exactly the same (including capitalization) both times. When done, press (F10) on the 100LX or (ENTER) on the 95LX. With the equation you just entered highlighted, move the cursor to the left and type a name for the formula (e.g. "Sale"). Now press (F9) (Calc). You'll see a screen similar to this:

Solver Screen: HP 95LX: Graphic

 Note that the labels above F2, F3, and F4 reflect the name of our variables. Let's say we came across an item priced at $49.95. Type 49.95 and press (F2) (ListPr). Then type .15 (for 15%) and press (F3) (Discou). Finally press (F4) (IPay) to reveal the sale price -- $42.46.

You can use this same formula any time in the future, no matter the discount or list price. Just change the numbers as you need them. To save your formulas on the 95LX, press (MENU) File Save and give a file name. The HP 100LX automatically saves formulas.


The Conversion application lets you convert length, area, volume, mass, and currency (the 100LX adds temperature conversion to this list). We can use the currency conversion option in a way not originally intended, to solve the example problem. In the process, we'll see how easy it is to use the conversion applications on the HP Palmtops.

Suppose you enter a store that is offering two different discounts. Some items are discounted 15% and others 25%. Let's see how the currency application can help.

On the 95LX press (MENU) Conv Currency. On the 100LX press (MENU) Application Conversion and select Currency. Now press (F2) (Edit). Press (F10) (More) until you get to the end of the currency conversion rates list. You should see five blank lines available for additional currency rates.

Currency Conversion List: Graphic

 Highlight the first available blank line, press (F2) (Name), type in List Price and press (ENTER). Use the same procedure to enter the names 15% Discount and 25% Discount on the next two available blank lines.

Move the cursor back up to List Price, key in 100 and press (ENTER). Next move the cursor to 15% Discount, key in 85 and press (ENTER). Move to 25% Discount, key in 75 and press (ENTER). Finally, press (ESC) and you're ready to go shopping.

Let's say you see a great pair of pants for $54.95. Move the cursor up to List Price, type in 54.95 and press (ENTER). You'll see the 15% discount price is $46.71 and the 25% discount price as $41.21.


We saw last issue that HP CALC's Arithmetic application is a powerful tool to solve a variety of arithmetic problems. This article displayed Arithmetic's ability to subtract a constant percentage by just typing a number and pressing (ENTER). The article also showed that four other HP CALC's applications could deal with that problem.

The Business Percentage application was designed to solve our discount problem. Use Business% to solve simple common percentage problems.

List is a simple and useful tool for adding a series of numbers and keeping track of their sum. The 100LX also automatically computes average and standard deviation and lets you work with two columns at once. In our example we added a number of discounted prices and automatically kept track of both the items and the sum.

Solver let us create a generic formula for solving our shopping discount problem. Solver can be used to solve a variety of simple or complex problems. It offers many features and functions and is worth delving into more deeply, especially for technical users.

Finally, we used Currency Conversion in a unique way. All of the conversion applications convert a number from one unit of measurement to another. The Currency conversion differs from the other conversion applications because the relative value of currencies fluctuates. The Currency conversion lets you assign relative values.

We used this feature to compute a 15% and 25% discount from a suggested list price.

HP CALC, like the HP Palmtop itself, is filled with rich features and capabilities. Spend a little time exploring it and the manual and you will find yourself using HP CALC more in your every day dealings.