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2. A prospective multicenter trial of the ovulation method of natural family planning: II. The effectiveness phase;World Health Organization;Fertil Steril.,1981
3. Periodic Fertility and Sterility in Women;Knaus,1934
4. The Rhythm Way to Family Happiness;Murphy,1955
5. A practical open-scale thermometer for timing human ovulation;Keefe;N Y State J Med.,1949