加線
Anon. 2001. "Leger [Ledger] Line". The New Grove Dictionary of Music and Musicians, second edition, edited by Stanley Sadie and John Tyrrell. London: Macmillan Publishers.
Godwin, Joscelyn. 1974. "Playing from Original Notation". Early Music 2, no. 1 (January): 15–19.
Oxford English Dictionary. 2005. "Ledger, n.B.I.3". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (要購読、またはイギリス公立図書館への会員加入。