A QUICKIE LESSON ABOUT CALCULATORS
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A calculator is a device that is used for performing mathematical calculations. It differs from a computer by having a limited problem solving ability and an interface optimized for interactive calculation rather than programming. Calculators can be hardware or software, mechanical or electronic, and are often built into devices such as PDAs or mobile phones.

Modern electronic calculators are generally small, digital, (often pocket-sized) and usually inexpensive. In addition to general purpose calculators, there are those designed for specific markets; for example, there are scientific calculators which focus on operations slightly more complex than those specific to arithmetic - for instance, trigonometric and statistical calculations. Some calculators even have the ability to do computer algebra. Graphing calculators can be used to graph functions defined on the real line, or higher dimensional Euclidean space. They often serve other purposes, however. Modern calculators are more portable than most computers, though most PDAs are comparable in size to hand-held calculators.