
In a different key's scale, the Major key intervals would follow the same pattern but would, obviously, occur between different note names, because your tonic or starting note of the scale will be different.You need to be aware of how scales are constructed to know which note to hit when you see a double flat or double sharp sign on the notation. The semi tones for C Major scale will occur between E and F intervals and the B and C intervals of the scale. But you need to play an extra sharp (or half tone up), so you'd play C# because the Major scale pattern is: Tone,Tone, Tone, Semi Tone, Tone, Tone, Semi tone, tone (adding up to 8 notes of this scale). This, in C Major key, if it is placed before b note,one half tone up takes the note to C.

I believe the X before a note means you play a double sharp.
