A hand-operated, battery-powered, electronic, instrument used for recording basal body temperature and cycle length to identify the fertile and infertile phases of the menstrual cycle. The device consists of a basal body temperature thermometer and a microprocessor programmed with a mathematical algorithm to calculate and identify temperature shifts. It is used to predict ovulation to optimize the chances for becoming pregnant or for determining safe periods where sexual intercourse may take place. It is typically a noninvasive, automatic device.