In music, a scale is any set of musical notes ordered by fundamental frequency or pitch. A scale ordered by increasing pitch is an ascending scale, while descending scales are ordered by decreasing pitch. Some scales contain different pitches when ascending than when descending (i.e. the chromatic scale and melodic minor scale). Often, especially in the context of the common practice period, part or all of a musical work including melody and/or harmony, is built using the notes of a single scale, which can be conveniently represented on a staff with a standard key signature. Due to the use of enharmonics, many notes have two names (use of a flat or sharp) -- and in some cases, have more than one type of accidental. Note the use of double sharps (x) and double flats (bb) in some music.