The basic function of chord symbols is to eliminate the need to write out sheet music. The modern jazz player has extensive knowledge of the chordal functions and can mostly play music by reading the chord symbols only. Advanced chords are common especially in modern jazz. Altered 9ths, 11ths and 5ths are not common in pop music. In jazz, a chord chart is used by comping musicians (jazz guitar, jazz piano, Hammond organ) to improvise a chordal accompaniment and to play improvised solos. Jazz bass players improvise a bassline from a chord chart. Chord charts are used by horn players and other solo instruments to guide their solo improvisations.