A read-create Integer32 (-1 to 255) specifying the slot number of the card acting as the primary in this failover group on a distributed device in standalone mode, with -1 used to delete the node. It lets an admin pin the primary side of a failover pair to a specific physical card slot, which is essential for chassis-based platforms with multiple interchangeable service cards. Setting this to slot 3 designates the card in slot 3 as the primary member of the failover group.