A double-pointed tone that raises a tone by two semitones (a whole tone). In terms of physical pitch, the compound increase of 1 is 2. It is indeed the same key on the keyboard. However, musically, we can't regard the rise of 1 as 2. If you pay attention to the music score (staff), you will find that the double-pointed sign usually only appears in key signature's music score of Key Signature, which consists of three or more pointed signs. That is, it only appears in a major and e major. . . Up to the score of #F major (or its relative minor).