Represents a note in an incorrect position. So, for example, if you're trying to find the tune FFAAB. You'll get three gears and two tumblers. If you guess CA. You'll get one tumbler. If you guess BBBBB. You'll get one gear. If you guess DDDDD. You'll get silence (in other words, no gears and no tumblers). If that's a gear, then we're done with the first position. We don't know if any more A. S are in the tune, so our next stab is AA. Back to the first play though: if A. If we get silence, then we know A.