Identification numbers with check digit algorithms 
Instructions
1. Move the green dot above to choose the module. For example, to choose module \(10\), you have to put it as in the following picture:
2. Suppose you would like to add \(6\) and \(8\) module \(10\). First, put the top orange dot in line \(6\) and column \( 8\). The orange dot, far below, points the value of the sum. In the figure above, it is equal to \(4\).
