It's listing all the available character devices for scanning. Each physical disk normally shows up at least twice, once for the entire device, ("disk0") and once for each formatted HFS+ partition on it. ("disk0s2", "disk0s5", etc)
This allows you to surface scan an unformatted disk, as well as to scan a specific disk by volume name if you don't know the device number.
In any event, no matter which "disk0" you select, it will scan the entire disk0 device.
In the past it was set up to only scan the specific partition if you selected one, but I decided that was silly since you really need to know if the entire drive the volume is on is bad, not just to see if there's an error on the specific partition. (since an error ANYWHERE on the drive can cause it to beachball when accessing ANY partition on the drive) My philosophy is that a drive with even one slow block or one bad block needs to be replaced immediately.
