A basal body temperature thermometer is used to measure a person's body temperature immediately upon waking in the morning. Compared to daily body temperature, basal body temperature is less affected by environmental factors such as exercise or eating. This is beneficial for detecting subtle daily changes in body temperature, such as during ovulation or changes in thyroid function.
Glass fever thermometers have a minimum scale of 0.2°F (0.1°C), while basal body thermometers require at least 0.1°F (0.05°C) accuracy. Therefore, glass basal body thermometers are sold separately from regular glass fever thermometers. However, all electronic thermometers have at least 0.1°F (0.05°C) accuracy and can therefore be used as basal body thermometers. Some digital thermometers are specifically labeled as 'basal body thermometers' and have special features, such as a large display screen, additional memory functions, or audible guidance for correct placement.
