Identification numbers with check digit algorithms 
Instructions
1. Move green dots, with mouse, to "write" the first fifteen digits of the visa card number. For example, in case \(1234\;\;5678\;\; 9012\;\;345\), we have to place the dots in the following manner:
2. The orange dot indicates the checksum digit of visa card. In the example in the figure above, it is equal to \(2\).
