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  A logarithmic device with rods divided into squares with ten numbers used for calculating multiplication and division.
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  A ruler that you slide the different parts to get the answer.
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  A rotating colmn with number. when the lower decimal place reset to zero it would change the one to the left by one.
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  A mechanical device that could do addition, subtraction, multiplication, and division.
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  Another mechanical calculator.
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  Another mechanical calculator
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  Never produced.
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  Never produced.
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  Calculated the 1890 census using punch cards
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  The first generation of computers used vacuum tubes. They burned out a lot. Programs were written in machine code.
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  Transistors Replace Vacuum Tubes. Operating Systems become possible.
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  Integrated circuits appear, allowing thousands of transistors on one chip
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  General-purpose microprocessors appear, allowing computers to do more than ever before, such as display graphical images.
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