Irving Berlin could not read music, he learned to play by ear. He also could not play the piano except in the key of  F# major on mostly the black keys. He bought a piano with twelve notches and a lever. When the lever was moved to a new notch the keyboard was moved to the next string. This was Berlin could play in different keys by still playing the keys on the keyboard that he was used to playing.

(The Great Courses – Great American Music: Broadway Musicals)