You may have noticed an F# note in the Blues scale in exercise 13. F# has exactly the same sound as Gb , and therefore either spelling of the note may occur in the written music. This is an example of enharmonic spelling of the same note. Here are some more examples of enharmonic notes.
This 12 bar Blues contains examples of two blue notes and their enharmonic alternatives: b3 (Eb = D# ) and b5 (Gb = F# ).