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Difference engines are strictly calculators. They crunch numbers the only way they know how - by repeated addition according to the method of finite differences. They cannot be used for general arithmetical calculation. The Analytical Engine is much more than a calculator and marks the progression from the mechanized arithmetic of calculation to fully-fledged general-purpose computation.

Physical Legacy Aside from a few partially complete mechanical assemblies and test models of small working sections, none of Babbage's designs was physically realized in its entirety in his lifetime. The major assembly he did complete was one-seventh of Difference Engine No. 1, a demonstration piece consisting of about 2,000 parts assembled in 1832. This works impeccably to this day and is the first successful automatic calculating device to embody mathematical rule in mechanism. A small experimental piece of the Analytical Engine was under construction at the time of Babbage's death in 1871. Many of the small experimental assemblies survived, as does a comprehensive archive of his drawings and notebooks. The designs for Babbage's vast mechanical computing engines rank as one of the startling intellectual achievements of the 19th century. It is only in recent decades that his work has been studied in detail and that the extent of what he accomplished becomes increasingly evident.

Babbage embarked on an ambitious venture to design and build mechanical calculating engines to eliminate the risk of human error in the production of printed tables. The 'unerring certainty of machinery' would solve the problem of human fallibility. His work on the engines led him from mechanized arithmetic to the entirely new realm of automatic computation. Tabular errors provided a practical stimulus. But this was not his only motive. He also saw his engines as a new technology of mathematics.

It was not only the grindingly tedious labor of verifying a sea of figures that exasperated Babbage, but their daunting unreliability. Engineering, astronomy, construction, finance, banking and insurance depended on printed tables for calculation. Ships navigating by the stars relied on printed tables to find their position at sea. The stakes were high. Capital and life were thought to be at risk.