It serves to find out the original personal identification in case the person received NID (alternative identification number) in case of duplicity. This identification is not unique. It contains:
- the birth number (9-digits birth number is padded on the right with a space) for Czech individuals,
- IC (organization identification number) padded on the left with zeroes to 10 characters for Czech legal entities,
- the birth date in format yyyymmdd padded on the right with 2 spaces for foreign individuals,
- the foreign identification number padded on the right with spaces to 10 characters (or blanks if it is not known) for foreign legal entities.