Billings, E., & Westmore, A. (1980). The Billings method of Natural Family Planning: Controlling fertility without drugs or devices (1st American ed.). Random House.
Chicago-referens (17:e uppl.)Billings, Evelyn, och Ann Westmore. The Billings Method of Natural Family Planning: Controlling Fertility Without Drugs or Devices. 1st American ed. New York: Random House, 1980.
MLA-referens (8:e uppl.)Billings, Evelyn, och Ann Westmore. The Billings Method of Natural Family Planning: Controlling Fertility Without Drugs or Devices. 1st American ed. Random House, 1980.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.