A calculator is one of those necessary tools used by children and adults alike. It eases the way through both simple and complex mathematics and aids in a quick calculation of numbers with extreme accuracy. The Casio Fx-115D is a black calculator designed for math and science. This pocket-sized calculator performs 228 functions and has the added benefit of being solar-powered rather than battery-powered, which gives you one less worry. Besides adding, subtracting, multiplying and dividing, its functions include trigonometric functions, hyperbolic functions, exponentials, logarithms and more.

Turn on the Casio Fx-115D calculator by pressing the "On" button. A "0" should show on the display. The calculator is already equipped with a solar cell and a lithium battery. Replace the lithium battery once every six years.

Press any numbers as desired for a basic calculation and use the plus, minus, multiply and divide buttons on the lower right hand side. Press "=" when you want to see the result.

Press "C" to clear the value and to re-enter the numbers when a mistake occurs.

Press "AC" to clear the display and to start a new calculation.

Select the Mode button located in the top right-hand corner to choose a certain operating mode. Then, you can select the dot button, Exp button or buttons 0 through 9. The dot button refers to engineering calculation mode which is displayed as ENG while the Exp button displays CMPLX, indicating a complex number calculation mode. Press the 0 button for COMP or ordinary arithmetic calculations, 1 for BASE-N or binary/octal/decimal/hexadecimal operations, 2 for LR or regression analysis and 3 for SD or standard deviation. Press 4 to display D as degrees, 5 for R as radians and G as grads, all as the unit of angle measurement. Press 7 and then any number from 0 to 9 to indicate how many decimal places to display (FIX), press 8 and any number from 1 to 10 to indicate how many significant digits to display (SCI) and press 9 to cancel the changes made by Mode 7 and Mode 8.

Check the display of the calculator to see if the appropriate mode is set. The mode will be displayed in the top line of the display, which is above the numbers being calculated, known as Mantissa. The right-hand side displays the exponent.

Press "Mode" and the chosen button again to cancel the operating mode in the calculator if necessary.

Use the digit buttons and the additional functions to perform basic and complex mathematical and scientific operations or calculations. Clear the display by pressing "AC" once you are done calculating. Refer to the Casio Fx-115D manual for detailed instructions on each of the functions. Always press a function, such as "sin," which stands for sine, first before pressing any numbers to get an accurate calculation.

Turn the calculator off by putting it away into a backpack or drawer, but not necessarily out of the light since it will function in darkness as well. The calculator's auto power-off function allows it to turn off automatically when not used for about 6 minutes.

#### Tip

Remember the order of basic calculations. A simple mnemonic for this is known as PEMDAS, which stands for "parentheses, exponents, multiplication, division, addition and subtraction." Keep the Casio Fx-115D calculator in a dry place at room temperature to avoid damage.