A YouTuber known as 3D all Workshop has designed and 3D-printed a working mechanical calculator small enough to hold in one hand. The device relies on a Leibniz stepped drum, a mechanism more than 200 years old, which is also found in the famous Curta "pepper mill" calculator. The drum's teeth of varying lengths allow numbers to be entered and added mechanically.
The calculator is capable of addition and multiplication, the latter performed as repeated addition. However, it cannot subtract or divide; the maker explained that there was not enough room in a palm-sized design for the additional mechanisms. The project was not without difficulty: roughly 100 design iterations over two months were needed to overcome problems such as gear binding, backlash, and parts breaking during use.
The final build consists of 109 separate pieces, took 17 print-hours to complete, and used 90 grams of filament. Despite requests from viewers, the design has not been published or sold. The project highlights how far 3D printing has come, while also showing the engineering challenges that remain for precise mechanical devices.