A difference engine is an automatic mechanical calculator designed to tabulate polynomial functions. It is viewed as a pioneer computing device and was created by Charles Babbage. There is quite a complex and intriguing story about how it came to be invented and then how the device came into being at around the year 2000. I’ll not go into that here though.
The difference engine is fascinating to watch, especially the back side, which reminds me of DNA‘s double helix. I added a youtube video of it operating that has a good background narrative.