Billings, J. J. <br/><br/>
The ovulation method of natural family planning. 

 - Rev. ed. 
 - Cork :  Ovulation Method Advisory Service,  1977. 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Birth control -- Popular works.--Birth control -- Popular works.<br/>Ovulation -- Popular works.--Ovulation -- Popular works.