A computer printer that was originally designed more than 150 years ago has finally been built and will go on display at the Science Museum in London.

Babbage's reputation has been vindicated, both as a visionary of the computer age and as an engineer of the most extraordinary calibre

Doron Swade

It is the final piece of a mechanical calculating device designed by the computer pioneer Charles Babbage. The 19th Century inventor was frustrated by the errors found in mathematical tables calculated by hand and set about building a machine that would do the job properly.

But Babbage, derided by those who thought the task impossible, never got to complete his Difference Engine, or the printer to run off the tables that were then widely used in navigation, engineering, banking and insurance.

It took the intervention of the Science Museum in 1985 to bring the project back to life.

Original blueprints

Working to the original designs, a team of engineers constructed a three-tonne calculating device, Difference Engine No 2, that was completed in 1991. It consists of 4,000 parts and works perfectly - just as Babbage intended.

Nine years on, the printer, which weighs in at an estimated 2.5 tonnes, has also been completed and is now undergoing final tests.

The printer is astonishingly advanced. It automatically prints the results of a calculation and can be programmed by the user to present information in different ways.

"You can arrange how many columns the results appear in," said Doron Swade, assistant director of the Science Museum, and a driving force behind the Babbage project." You can even arrange the height between the lines, the space between columns and leave gaps between lines to make the results easier to read. The lines also wrap."

Industrial espionage

The apparatus not only provides a printed paper record but also produces stereotype plates for use in a conventional printing press.                                                  

Much of the building work was done by engineer Reg Crick. He said Babbage's design was perfect except for what are now thought to have been some deliberate errors intended to foil spies." There were some mistakes, but we think he was afraid of industrial espionage," he told the BBC. "We think Babbage deliberately put errors into the drawings to mislead anybody that might try to sell them."

A book, The Cogwheel Brain, about Babbage's quest to build a calculating engine, has been written by Doron Swade to coincide with the unveiling of the new printer. "Babbage's reputation has been vindicated, both as a visionary of the computer age and, more specifically, as an engineer of the most extraordinary calibre," Mr Swade said.