# Basic Operation of the Calculator

Before you begin working problems on the calculator, there are a few special features of it that you should know. These features are:

After you have reviewed each of these, test your skill to see if you have mastered the features.

## Basics of Time Value of Money Calculations

Once you have understood the function of the basic operations of the calculator above, you may proceed to learn the Basics of Time Value of Money Calculations

Multiple function of keys--In order to allow the HP10B calculator to fit conveniently into a pocket, it was necessary for each key to do double duty. This double duty is accomplished by the key serving one function when it is pressed by itself, or another function if the cream colored key is pressed in combination with the key. As you will note, above every key is written the second function for that key. To activate that function, simply press the cream colored key first, then the key where that function resides. back to the top

Rounding--The HP10B calculator stores numbers internally to many decimal points. However, you choose how many decimal points the calculator display will show. In working problems, you should remember that even though you may have set the calculator to perhaps display only two decimal places, the actual number the calculator uses has many more. This will sometimes result in a small rounding error. For example, if you borrowed \$1,000 from a bank for two years at 15% interest, your monthly payment would be \$48.49. When you solved this problem, the calculator display would show 48.49 if you set the number of decimal points to display at two. However, the actual number stored in the calculator is much more precise. If you changed the number of decimals to display to nine, the number would be 48.486648047. The number actually stored in the calculator has several more decimal levels of precision. If you find the rounding error unacceptable, you must reenter the payment as exactly \$48.49 or simply hit the RND key (the cream key and back arrow key combination). Most of the time, however, you will not need to worry about the small rounding error. In this particular problem, the error results in an overpayment of \$.08 over the two year life of the loan. back to the top

Constant memory--The HP10B calculator has a constant memory. This means that when you enter a number into the calculator, that number stays there even when the calculator is turned off until one of three things happen. Either you clear the calculator, your batteries die, or you get frustrated and throw the calculator against a wall and shatter it into many pieces (not recommended!). This constant memory feature is very useful when working multiple part problems that require recalculation after changing one or two numbers. The other numbers will not need to be reentered. This helpful feature can sometimes cause a problem, however. If you fail to completely clear your calculator when you begin a new problem, there may be a number previously stored that will give you an incorrect answer when you solve for the answer to the new problem. To avoid this difficulty, simply hit the clear all keystroke combination. back to the top

Storage memories--A very handy feature of the HP10B calculator is the ability to store up to twenty numbers in the calculators storage registers. This feature is particularly useful when working longer, more complicated problems where there are several steps and various intermediate results that must be used later in the problem. Rather than writing those intermediate results on a paper, you can simply store them in one of the calculator's storage registers. To store a number simply press the cream colored key, the STO key, and then the number of the storage register you desire. The storage registers are numbered from 0 to 9 and from .0 to .9. To recall a number you have previously stored, press the RCL key and that number. back to the top

Setting the number of decimal points in the display--Setting the number of decimal points in the display of the HP10B calculator is a very easy task. All that is necessary is to press the cream colored key, the DISP key, and then the number of decimal places that you would like to see. back to the top

Clearing the calculator--The Hp10B calculator has three clear functions. To clear the last digit that you have just pushed, press the back arrow key located at the third row down on the far right column. To clear all of the number in the display, press the clear key located at the bottom left corner. To clear all or the values stored in the calculator, you must first press the cream colored key and then the input key. This key combination activates the clear all function. You may wish to use the clear all function when you first begin working a problem. back to the top| back to constant memory |back to time value of money basics

Changing the sign of a number in the display--When working a time value of money problem, the HP12C calculator keeps track of the direction money is flowing. For example, if money is being received, that amount is indicated as a positive number. If, on the other hand, the money is being paid, that amount is indicated as a negative number. Thus, money received is positive and money paid is negative (just like real life!). When working a problem, you may need to tell the calculator the direction of the cash flow. To change a number in the display from positive to negative or from negative to positive, all you need to do is press the key. back to the top

Automatic inactivity power down--The HP10B calculator is equipped with an automatic power down feature in order to conserve batteries. If the calculator is left unused for several minutes, it will automatically turn itself off. All numbers stored in the calculator other than the number in the display are preserved. back to the top