1. The Ovulation Method;Billings,1974
2. The Ovulation Method. The symptom pattern of fertility;Billings;Acta Med. Rom.,1978
3. Symptoms and hormonal changes accompanying ovulation;Billings;Lancet,1972
4. Timing of ovulation;Brown;Med. J. Austr.,1977
5. Midcycle hormonal profiles, cervical mucus and ovulation;Casey,1977