Identification numbers with check digit algorithms 
Instructions
Suppose you would like to add \(7\) and \(8\) module \(12\).
1. Rotate the orange dot to choose number \(7\).
2. Rotate the green dot (the one far in the right) to choose number \(8\).
3. Rotate the green dot far in the left and put it below orange dot, as in the following picture:
4. The sum value is marked in red on the "clock". In the example above, it is equal to \(3\).
