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A calculator is a device that performs arithmetic operations on numbers. The simplest calculators can do only addition, subtraction, multiplication, and division. More sophisticated calculators can handle exponent ial operations, roots, logarithm s, trigonometric functions, and hyperbolic functions. Internally, some calculators actually perform all of these functions by repeated processes of addition.Most calculators these days require electricity to operate. Portable, battery-powered calculators are popular with engineers and engineering students. Before 1970, a more primitive form of calculator, the slide rule , was commonly used. It consisted of a slat of wood, called the slide, that could be moved in and out of a reinforced pair of slats. Both the slide and the outer pair of slats had calibrated numerical scales. A movable, transparent sleeve called the cursor was used to align numerals on the scales. The slide rule did not require any source of power, but its precision was limited, and it was necessary to climb a learning curve to become proficient with it.

One of the most primitive calculators, the abacus is still used in some regions of the Far East. The abacus uses groups of beads to denote numbers. Like the slide rule, the abacus requires no source of power. The beads are positioned in several parallel rows, and can be moved up and down to denote arithmetic operations. It is said that a skilled abacus user can do some calculations just as fast as a person equipped with a battery-powered calculatorAs calculators became more advanced during the 1970s, they became able to make computations involving variables (unknowns). These were the first personal computers. Today's personal computers can still perform such operations, and most are provided with a virtual calculator program that actually looks, on screen, like a handheld calculator. The buttons are actuated by pointing and clicking.

Theoretically, a modern computer is a calculator that works with binary numbers and has a much larger memory. But in the practical sense, a computer is far more than a mere calculator, because of the wide variety of non-computational tasks it can perform