Success, it is often said, has many fathers—and one of the many fathers of computing, that most successful of industries, was Charles Babbage, a 19th-century British mathematician. Exasperated by errors in the mathematical tables that were widely used as calculation aids at the time, Babbage dreamed of building a mechanical engine that could produce flawless tables automatically. But his attempts to make such a machine in the 1920s failed, and the significance of his work was only rediscovered this century. Next year, at last, the first set of printed tables should emerge from a calculating 'difference engine' built to Babbage's design. Babbage will have been vindicated. But the realization of his dream will also underscore the extent to which he was a man born ahead of his time. The effort to prove that Babbage's designs were logically and practically sound began in 1985, when a team of researchers at the Science Museum in London set out to build a difference engine in time for the 200th anniversary of Babbage's birth in 1992. The team, led by the museum's curator of computing, Doron Swade, constructed a monstrous device of bronze, iron and steel. It was 11 feet long, seven feet tall, weighed three tons, cost around $500 000 and took a year to piece together. And it worked perfectly, cranking out successive values of seventh-order polynomial equations to 31 significant figures. But it was incomplete. To save money, an entire section of the machine, the printer, was omitted. To Babbage, the printer was a vital part of design. Even if the engine produced the correct answers, there was still the risk that a transcription or typesetting error would result in the finished mathematical tables being inaccurate. The only way to guarantee error-free tables was to automate the printing process as well. So his plans included specifications for a printer almost as complicated as the calculating engine itself, with adjustable margins, two separate fonts, and the ability to print in two, three or four columns. In January, after years of searching for a sponsor for the printer, the Science Museum announced that a backer had been found. Nathan Myhrvold, the chief technology officer at Microsoft, agreed to pay for its construction (which is expected to cost $373,000 with one proviso: that the Science Museum team would build him an identical calculating engine and printer to decorate his new home on Lake Washington, near Seattle). Construction of the printer will begin—in full view of the public—at the Science Museum later this month. The full machine will be completed next year. It is a nice irony that Babbage's plans should be realized only thanks to an infusion of cash from a man who got rich in the computer revolution that Babbage helped to foment. More striking still, even using 20th-century manufacturing technology the engine will have cost over $830 000 to build. Allowing for inflation, this is roughly a third of what it might have cost to build in Babbage's day-in contrast to the cost of electronic-computer technology, which halves in price every 18 months. That suggests that, even had Babbage succeeded, a Victorian computer revolution based on mechanical technology would not necessarily have followed. Babbage wished to build a mechanical engine because______.