D3. Standard. Seltmann, Werner and Angerhöfer, Günter. Fagott-Schule in sechs Bänder, vol. 6 (Mainz: Schott), p. 132. Permission granted for inclusion in this WWW index by Deutcher Verlag für Musik.
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D3. Ewell, Terry B. (05 October 1996). Source unknown. For sharper pitch.
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D