|  | GeoAstro Applets | Astronomy | Chaos Game | Java | Miscel- laneous | 
| Genaille–Lucas rulers (also known as
              Genaille's rods) is an arithmetic tool invented by Henri
              Genaille, a French railway engineer, in 1891. The device
              is a variant of Napier's bones.  Example: 874 : 7 Start reading the result by the first number in the column of dividend's first digit, and in the row of the divisor (7), and follow the lines:   874 : 7 = 124 R 6 | 
