A difference engine only needs to be able to add.

What I need, he thought, is to get to the university and liberate one of their difference engines.

A difference engine can be patented because it is a physical device.

What use is a difference engine if not to perform math calculations?

You would use cogs or Meccano to make a difference engine.

The difference engine is the same as the one used in MediaWiki.

By developing something better, Babbage had rendered the difference engine useless in the eyes of the government.

In 2000, the printer which Babbage originally designed for the difference engine was also completed.

In 1991, a perfectly functioning difference engine was constructed from Babbage's original plans.

There were still constructs and difference engines in the city, but far fewer, strictly licenced.