There are many inexpensive scientific calculators on the market, but few boast the two-line display and other advanced features users get with the TI-30x IIS. The display shows the equation you are creating on the top line, and the numbers or symbols you are currently entering on the second line. Once the equation is solved, the results are displayed on the second line, and you can use the four arrow keys on the front of the calculator to edit the original equation in any way you like for a recalculation. Better still, pressing the up arrow repeatedly lets you browse through a cache of dozens of previous calculations, meaning you can look back to see the answer to a problem you solved two minutes ago, two days ago, or whenever. This is a calculator for science, math, algebra, trigonometry, statistics. 2-Line Display, 5 Memories Enter/delete/insert/edit individual statistical data elements Trig functions in degrees and radians Fractions and Fraction/Decimal conversions Degrees, Minutes, Seconds (for time calculations) Decimal degree conversions Common natural logarithms Reciprocals and Factorials Universal Powers and Roots Polar/Rectangular conversions Menus User-friendly keyboard with durable, plastic keys Protective calculator shield. The device uses solar power when possible but can fall back on the internal batteries (which are included) if there isn't enough light. The buttons wiggle around a little too much and require a firm keystroke to register input, but the fact that input can be followed by looking at the output on the first line helps to cut down on mistakes. There is a shift key that doubles the functions of most buttons, and although the TI-30X IIS isn't festooned with as many buttons or functions as some other calculators we've tested in this price range, it's still very capable. There are three angle modes (degrees, radians, and grads), scientific and engineering notation modes, and even one- or two-variable statistical modes. Five variables can also be assigned to their own memory slots. The documentation is lacking, as everything is presented on a single folded sheet of paper, but Texas Instruments did manage to pack several illustrated examples on the page. The calculator comes with a snap-on cover that fits on the back of the device when you are using it.