Doing Arithmetic on Your HP Palmtop

Using HP CALC to do arithmetic is easy and powerful once you learn a few tricks and the meaning of a few words.

By Hal Goldstein

Since the inception of electronic calculators, the HP's Corvallis division has assumed the lead in producing state-of-the-art calculators. This same division created the HP Palmtops. Therefore, it is not surprising that HP Palmtops contain a powerful advanced calculator.

It's easy to whip out your Palmtop and convert dollars to yen or use the List function to add a list of numbers. It's even pretty simple to use the Time Value of Money function to determine payments when refinancing your home.

Despite the ease with which these more involved tasks can be performed, many users shy away from using the HP Palmtop CALC application to do simple arithmetic. They either use Lotus 1-2-3 (if they are already familiar with that program), or pull out a pocket calculator.

My feeling is that users don't use HP CALC for arithmetic because the main screen is either barren of information or is so full it's intimating.

Using CALC's Arithmetic Function

Start CALC's Arithmetic function. On the 95LX press (HPCALC) Menu Arithmetic. On the 100LX press (HPCALC) Menu Applications Arithmetic (or (HPCALC) (CTRL)-A). You'll see one of the two following screens. [Editor's Note: We're using 100LX screen displays. The displays on the 95LX are almost identical.]

HP Calc's Opening Screen:  Graphic

HP Calc with Stack and Registers Displayed:  Graphic

 The barren screen shows the numbers involved in the current calculation in the lower right corner. HP calls this the Calc line (Graphic 1).

To get the second screen (Graphic 2), on the 95LX press (F2) (SHOW), on the 100LX press (MENU) Options Modes S(t)ack R(e)gisters). This more intimidating screen displays the current HP CALC "Stacks" and "Registers".

Unfortunately for the uninitiated, HP chose to use computer science jargon rather than common English. Instead of "stack", HP could have used "previous results"; instead of "registers", "stored numbers".

With the intimidating stack and register screen displayed, let's do some simple arithmetic. First, add 10 and 5 by typing 10+5= . (You can press (ENTER) instead of equal, but for consistencies sake, we'll use =.)

How the Stack Operates:  Graphic

More Details about Stack Operation:  Graphic

 Notice that the result 15 appears on the Calc line. Now let's divide 9 by 3 (type 9/3= ). Notice that the 15 moves up and is displayed across from (1) = (Graphic 3). The result of the previous calculation is always stored in this position in the "Stack." (Using the jargon of HP CALC, the previous calculation is the "top" of the stack, or the "y" value).

Now do the following calculation: 9*(4+6)= . The last result 3 moves to the (1) position, (the top of the stack), and 15 moves down the stack to the (2) position (Graphic 4).

Similarly, if we just start typing a new calculation, say by typing 8, we now have a list of previous calculations (a stack) that looks like this.

Stack: (3) = 15.00

(2) = 3.00

(1) = 90.00

Now suppose we want to add the last result, 90, to the 8 that we just entered. Simply type + B = (B (Last) enters the result of the last calculation, i.e. the number stored in Stack (1)).

The B (Last) key as well as the C (xy) and V (R) keys can be used to switch the numbers between the Calc line and the stack. Press C (xy) to switch the results of the current and previous calculations (i.e. the Calc line and Stack (1) are switched). Press the V (R) key to move the result of the previous calculations into the Calc line. When you press V, the results in the current Calc line are moved to Stack (3). Press V four times and watch the previous calculations cycle through. The best way to become familiar with these functions is to experiment.

Storing Numbers in Registers

The store number (in a register) function is probably more useful to most users. You can store up to 10 numbers for later retrieval into any of the built-in applications.

Let's look at a few examples to make this capability more clear. Suppose we owned two pieces of land, the first 500 by 150 feet. Let's calculate the land area in square meters.

First we enter 500*150= and get 75,000. Let's store that result in register 0 (storage place number 0). [Note the word "STO" below the N key. To store the results of a calculation, press this key followed by the storage location. I'll indicate this in instructions below as STO followed by a number, not N followed by a number. Likewise, I'll indicate the Recall function as "RCL," not the letter "M."]

With 75,000 on the Calc line, type STO 0. We also could have stored it in registers 1, 2, 3, 4, 5, 6, 7, 8, or 9 for later recall.

Now suppose we also own another 350 foot by 475 foot parcel of land. We type in 350*475= and come up with 166,250 square feet. To make sure we don't lose it, let's store that number in register 1 (type STO 1).

Let's say we want to see the area in metric units (meters). On the 95LX press (MENU) Conversion Area. On the 100LX press (MENU) Application C(o)nversion Area (ENTER). At the bottom of the screen 166,250 is still displayed. Now tell your Palmtop the units associated with that number. On the 100LX press (F4) (foot). On the 95LX press (F5) (Sq Ft). The Area Conversion screen shows that 166,250 square feet equals 15,445 square meters.

Adding Numbers in Registers

Now let's add our two parcels of land together and figure out the total in square meters. Go back into Arithmetic mode. With 166,250 on the Calc line, press +RCL 0= (letter for recall, 0 the register). We have a total of 241,250 square feet. On the 100LX press (F4), on the 95LX press (F5) and check the appropriate row to see that you have 22,413 square meters.

The above example illustrates the following points:

  1. 1. We can press RCL followed by a register number to recall a stored number in any register.
  2. 2. We can recall a stored number in an HP CALC application.
  3. 3. We can add a stored number to the current total at the Calc line.



"M" Stands for "Memory"

Many people don't know how to use a calculator's M key. "M" stands for "memory," and it refers to a place to store a number (like the registers on the Palmtops). In HP CALC, the M key is register 0. You can use the STO and RCL keys (as we did above), or the F7 to F10 keys to access this memory.

Pressing (F7) (M) is the same as pressing STO 0 because it stores the Calc line in Register 0. Pressing (F8) (RM) is the same as pressing RCL 0 because it recalls data stored in Register 0. In the earlier example we figured out the total area of our land. We could have done the same thing by typing RCL 1 + (F8) =.

The F9 (M+) and F10 (M-) keys simply add or subtract the number on the Calc line to whatever is in register 0. For example, if we wanted the total square footage of the two properties to reside in register 0, we would enter RCL 1 (F9). Notice how the value in the Reg0(M) line at the top of the screen changes.

Using Advanced Features

Now that you understand the basics, let's look at how you can easily use the advanced features in HP CALC's arithmetic model.


Let's say you're shopping at a store that's having a one-day 15% off sale and you're using your Palmtop to compute prices. You see a $140 item. To calculate the 15% discount, you would simply key 140-15%= to get the answer 119.

When a + or - sign precedes a percentage, the percentage is applied to the number preceding the sign and then added or subtracted. In the example above, 15% of 140 is subtracted from 140.

Note that this technique does not work with multiplication and division. CALC's Arithmetic function interprets 140*15%= as 140 times 0.15 (not 140 times 15% of 140). You get 19 as the answer, not 2,940.


This feature makes it easier for you to perform the same calculation over and over again. Let's say you want to subtract 115 from a series of numbers. If the first number was 333, you'd key in 333 - - 115= (two minus symbols) to arrive at an answer of 218. When you enter the minus symbol twice, CALC stores the number that follows it as a constant to be subtracted. Now, to subtract 115 from 601, all we do is key in 601 = to get 486.

You can do the same thing with percentages. An earlier example showed us how to subtract a percentage of a number to itself. We can incorporate the automatic constant into this technique as follows.

Let's say we want to subtract 15% of 140 from 140. We key this in as 140 -- 15%= (two minus symbols) to arrive at 119. Now to subtract 15% of 179 from 179 all we need to key is 179= to get 152.15.

Constants are Displayed in Brackets in HP Calc:  Graphic

 Note that the constant shows up on screen in brackets. To eliminate the constant, press (-) or (DEL).

You can use +, -, *. /, or ^ as operators in automatic constants.


Let's say you want to copy the results of a calculation into a letter you're writing in MEMO.

First, copy the results in the Calc line into memory: On the 95LX press (CTRL)-(F2); on the 100LX press (Fn)-(=). Next go into MEMO and position the cursor a the location you want the results to appear. Finally, paste the results in: On the 95LX press (F4); on the 100LX press (Fn)-(+).


If you use the copy and paste method described above to transfer HP CALC data to your Lotus spreadsheet, the data is treated as a label (text) by Lotus.

There is another way to move numbers from HP CALC into Lotus 1-2-3 using an 11th storage register. First, make sure you have 1-2-3 open. Go back to HP CALC and complete your calculation. Then press STO @ on the 95LX, or STO (<Spacebar>) on the 100LX and you're automatically transferred to Lotus. Move the cursor to the cell in which you want to copy the number and press (ENTER). The result is placed in your spreadsheet as a number, not a label.

Leave the Calculator At Home!

Once you get used to them, the percentage and automatic constant features can make you're life a lot easier. But even if you don't take advantage of HP CALC's advanced features, the Palmtop still does simple arithmetic like a champ!

Leave the calculator at home. You've got more math power than you'll ever need with an HP Palmtop in your pocket.