Pascal's Calculator
A French mathematician and experimental physicist - that's Blaise Pascal, one of the first modern scientists who developed and built calculator. He devised a calculating machine in 1645 that was capable of adding and subtracting numbers. The machine was operated by dialing a series of wheels approximately the size of a cigar. It has a hand-cranked mechanical gear system of which a series of 10-toothed wheels or dial represents a decimal numbers. Pascal's machine was actually capable of adding and subtracting numbers up to eight digits - it is capable of computing by counting integers. When a wheel is turned from 9 to 0, the next wheel to the left moved one digit. Addition was performed by hand turning the appropriate wheels by the amount to be added, while you do the reverse to perform subtraction.
Slide Rule by Oughtred
A slide rule is consists of two movable rulers placed side by side. Each ruler is marked of in such a way that the actual distance from the beginning of the rulers is equally proportioned to the logarithms of the numbers printed on the ruler. Once can easily and quickly multiply or divide by sliding the rulers. It was extensively used by engineers, technicians and scientists as well up to the early part of 70's. Its invention in 1620 was attributed to William Oughtred, an English mathematician.
Leibniz's Calculator
Like Pascal, Gottfried Leibniz, was a 17th century scientist who gave value and importance in building machines that could do mathematical operations with lesser labor and so he developed what became known later as Leibniz's Wheel or Calculator. He completed this in 1694. It actually utilized the same techniques for addition and subtraction as Pascal's device but in addition, Leibnitz's calculator can also perform multiplication and division and the most amazing is that it could extract square roots.
Babbage's Engine
Considered as the Father of Modern Computer, Charles Babbage, a 19th century English man designed an analytical engine which aimed to perform complex mathematical operations and print out results. It was never completed that time because of technical capabilities but it laid the foundation to the modern computers. Babbage original design contained all the basic elements of modern general-purpose computers. These include arithmetic control, logical unit, output and input data and calculations based on a sequence of instructions.
