Genaille-Lucas Rulers are pretty cool. They are a clever calculator that you can use to multiply some pretty big numbers.
MathHappens summer staff member Anh Nguyen made a colorful jumbo set from scratch in Corel Draw that you can download and print — its in 3 pages but be careful of the sizing or use the one page below: Page 1, Page 2, Page 3. Feel free to copy, explore, and use. It’s a great project to try to reverse engineer and figure out how they work. (You can also check the wikipedia for some hints)
Post update: A reader, Seika Abe found an error in one of the rods and so we made this corrected one page PDF . You can make some really nice sets like these with multiple rods per set printed onto paper or cardstock. There are also some good tips about the tool to cut the corners and fanning powder to make them slide better. Thank you Seika Abe.
“Miraculously, the rulers of the new version printed in A4 fits a tooth brush case as the bottom left part of the attached picture shows!The number 2750 specified by the four rulers is my nick name, that is, 2750 is denoted ABE as Hexa-decimal notation. I have printed “Genaille Lucas rulers one page.pdf” in a thick and mat A4 paper for inkjet printers and divided it into rulers with a cutting machine.To make each edge round accurately, I used a tool named Kadomaru https://amzn.to/3y0tJhS (shown upper left) and to improve slippery of the rulers, a powder named “fanning powder” usually used magicians forcard decks is also used. This mysterious and beautiful rulers is to be a Christmas present for my students!”