1. Move the green buttons with the mouse to "write" the Fiscal Identification Number (NIF). For example, to write the number \(118666070\), we have to put the buttons in the following way:
2. The first orange button indicates the checksum digit in NIF, while the second one indicates the checksum digit that the number should have (if the system would be well designed). In the example above, they are \(0\) and \(X\), respectively.