A basal thermometer is an ultra sensitive thermometer that tracks the body’s minutest temperature shift. A basal body temperature (BBT) thermometer is often used by women to chart their basal body temperature chart and hence to predict their fertile period or ovulation. A basal thermometer is more reliable and accurate than a simple glass thermometer since glass thermometers are only accurate to .2 degrees Fahrenheit whereas a basal thermometer is generally accurate to .1 degrees Fahrenheit.
The basal thermometer is used to chart a woman's fertile time of the month and is used in connection with a chart. The chart should show low temperatures before ovulation in the follicular phase, and higher ones after ovulation in the luteal phase. Using a basal thermometer in connection with a chart over several months should show the best times when conception can take place and enable the planning of intercourse or artificial insemination. However, times may vary slightly each month so that the user will need to check her temperature continually to ensure that she has the most accurate information. For this reason, some women prefer to use the basal thermometer in conjunction with other methods to ensure complete accuracy.