This counts ATM cells successfully transmitted out of this card's ports. As the outbound cell-level counterpart to cardInCells, comparing the two over the same window on a card handling mostly pass-through traffic reveals whether cells are being dropped somewhere in transit through the card, since a healthy transit card should show roughly matched in and out cell counts. For example, a persistent gap between cardInCells and cardOutCells on a transit card, larger than expected discard counters explain, would prompt an admin to look for an unaccounted internal drop point.