whole step so it is enharmonically equivalent to a G. Usage varies on how to notate the situation in which a note with a double sharp (or flat) is followed in the same measure by a note with a single sharp (or flat). Some publications simply use the single accidental for the latter note, whereas others use a combination of a natural and a sharp (shown below), with the natural being understood to apply to only the second sharp. The double accidental with respect to a specific key signature raises or lowers the notes containing a sharp or flat by a semitone. For example, when in the key of C minor or E major, F, C, G, and D contain a sharp. Adding a double accidental (double sharp) to F in this case only raises F by one further semitone, creating G natural. Conversely, adding a double sharp to any other note not sharped or flatted in the key signature raises the note by two semitones with respect to the chromatic scale. For example, in the aforementioned key signature, any note that is not F, C, G, and D is raised by two semitones instead of one, so an A double sharp raises the note A natural to the enharmonic equivalent of B natural. Courtesy accidentals In modern scores, a barline cancels an accidental, with the exception of tied notes. Courtesy accidentals, also called cautionary accidentals or reminder accidentals are used to remind the musician of the correct pitch if the same note occurs in the following measure. The rules for applying courtesy accidentals (sometimes enclosed in parentheses) vary among publishers, though in a few situations they are customary: When the first note of a measure had an accidental in the previous measure After a tie carries an accidental across a barline, and the same note appears in the next measure When a chord contains a diminished or augmented octave When there is a cross relation with another part Publishers of free jazz music and some atonal music sometimes eschew all courtesy accidentals. Microtonal notation Composers of microtonal music have developed a number of notations for indicating the various pitches outside of standard notation. One such system for notating quarter tones, used by the Czech Alois Hába and other composers, is shown on the right. In the 19th and early 20th centuries, when Turkish musicians switched from their traditional notation