Auto-Numbering of cards is an option that's available for all Task Boards and Scrum Boards; it can be helpful for teams that are dealing with large boards where the cards are all of the same type, or have similar names.
An example would be a Help Desk that's using Kerika to manage trouble tickets: they may have literally hundreds of cards, past and present, that are all called "Password reset requested". In situations like this, referring to "Card 1057" will be much more convenient.
Auto-Numbering is not turned ON by default for any board, but the Board Admin (or Account Owner) of any board can turn it on (or off) at any time using the Board Settings dialog that appears when you click on the gear icon on the top-right corner of every Task Board and Scrum Board:
Kerika keeps track of how many cards have been entered on a board so far, including cards that are now in Done or Trash, and it uses this to figure out the number for the next new card that's added to the board.
The numbers are kept as a separate attribute of each card, so they cannot be edited by anyone (including Board Admins); this helps ensure the integrity of the numbering system doesn't get compromised by any user's editing errors.
When you turn ON auto-numbering, Kerika starts displaying numbers on cards; when you turn auto-numbering on.
Card numbers are always unique to each board: a card with number 100 on Board A will have no relation with a card numbered 100 on Board B.
Since each board keeps track of its own sequence of card numbers, if you move a card from a Scrum Board back to the Backlog column it will lose the number it previously had.
That’s because once a card goes back into a shared backlog, we can’t be sure which board it will get pulled into the future: the card may return to the same board where it was originally located, or it may get pulled into a different Scrum Board. The smart approach in this situation is to reset card numbers when cards go back to a backlog, and that's what Kerika does.