Symptothermal methods (STM) of NFP use multiples observations to check for signs of fertility. They most commonly use a triple check system that includes basal body temperature, cervical mucus, and cervical position. Women are instructed how to make observations of these three signs, note them in their charts, and interpret their findings. The triple check system gives women an extra resource when another sign may be affected (i.e. a fever that throws off their temperature).