Identification numbers with check digit algorithms 
Instructions
1. Move the green button above to choose the sum module. For example, to choose mod \(9\), we have to put green button as in the following picture:
2. Suppose you want to multiply \(5\) and \(6\) mod \(9\). First, find the square in row \(5\) and column \(6\). Observe its colour and the corresponding number. In the picture above, the colour is green and, therefore, the result is three.
