The Fertility Thermometer measures Basal Body Temperature, or BBT. BBT is defined as the lowest natural, non-pathologic body temperature recorded after a period of rest, and a small spike in this temperature (just 0.5 - 1.0 degrees Fahrenheit!) can indicate that ovulation has occurred. Tracking your BBT every morning (before you get out of bed!) allows you to track your cycle, identify when ovulation has occurred, and calculate the window when you are most likely to conceive. This thermometer has the ability to sync with the Premom app in your phone automatically, making it easier than ever to record BBT data and seamlessly identify your fertile window. You can use the thermometer to time intimacy and help maximize your chances of conceiving!