Building a 5-ton mechanical calculator... from 19th-century plans

Starting in May, many will have the opportunity to see for themselves how they did computing the old-fashioned way: with lots of gears, a big crank and some muscle.

The Computer History Museum, in Mountain View, Calif., will unveil a new construction, the first in the United States, of the 19th century British mathematician Charles Babbage’s Difference Engine No. 2, an improved version of his earlier mechanical digital calculator.

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