Identification numbers with check digit algorithms 
Instructions
Suppose you would like to add \(7\) and \(8\) module \(12\).
1. Move the green dot above to choose number \(7\).
2. Move the orange dot above (far in the right) to choose number \(8\).
3. Move the orange dot (below) far in the left and put it below green dot, as the following picture shows:
4. The final result is indicated in red. In the example above, it is equal to \(3\).
