Identification numbers with check digit algorithms 
Instructions
1. Move the green dot above to choose the module. For example, to choose module \(7\), you have to move the dot as follows:
2. Suppose you want to sum \(3\) with \(5\) module \(7\). First, pick the square in line \(3\) and column \(5\). Observe its colour and then the corresponding number. In the picture above, the square is orange and, therefore, the sum value is one.
