Basal Thermometer for Natural Family Planning. This Basal Thermometer is a quality medical device used to aid in the monitoring and tracking of basal body temperature. With proper care this advanced thermometer will provide years of accurate measurements. Multifunctional Thermometer ? This highly accurate (1/100th Degree) thermometer doubles as a basal thermometer to aide in the family planning process or as a more reliable general thermometer to measure fever.