Genaille–Lucas rulers

Genaille–Lucas rulers are tools used for doing quick calculations, especially for multiplication and division. They are made up of lines, each of which is divided into small spaces. Each line also has numbers written inside the little spaces. By using these pieces, it is easy to do calculations in your head without using a calculator. For example, if you wanted to know what 7 times 8 is, you would look at the ruler and find the number 7. Follow the line until you find the number 8. Where the two lines meet is your answer: 56!