A YouTuber 3D printed a working mechanical calculator out of 109 pieces, and it only adds and multiplies... The maker behind the YouTube channel 3D all Workshop spent two months building a pocket calculator with no metal springs, no screws and nothing he couldn't make on his 3D printer (his video). His description puts the cost at $2 in plastic and a bit of oil. The Register called it a working, but limited, build. The limits were his call. He wanted it to fit in a pocket, and he says subtraction and division would have made it too big and too complicated, so it adds and multiplies. You can enter up to 999, and multiplying is the same number added over and over with a crank while a counter tracks the turns, which is how the Curta does it too (The Register). Inside is a part more than 200 years old, the stepped drum named for Gottfried Wilhelm Leibniz. Each drum has nine teeth of different lengths, one drum per digit, and a lever moves a gear along it so the crank only catches as many teeth as the number you picked (The Register). The first print didn't work. In his video he says the tiniest printing inconsistencies made parts too tight or too loose, holding it knocked gears around, and slack between gears pushed the drums out of sync. He switched to a 0.2 mm nozzle, went through what he calls hundreds of prototypes, printed his own springs and added a ratchet so the crank turns one way only. The finished build is about 109 parts, 17 print hours and 90 grams of filament. You can't print this one, since The Register reports he hasn't released the design despite people asking. If you print anything with moving parts, I'd still watch his troubleshooting chapter. He used supports only where he had to, because every supported surface came out rough and added friction. He admits it's nowhere near as practical as a normal calculator. It still multiplied 421 by 4 and landed on 1,684 (his video).