A thermometer is a device that measures temperature or a temperature gradient.Using a thermometer to check your temperature can help you manage an illness. A rise in your temperature is usually caused by an infection or fever.
Normal body temperature
Normal body temperature is about 98.6 degrees Fahrenheit (°F) or 37 degrees Celsius (°C). Your temperature often varies from 1 to 2 °F or ½ to 1 °C. Your temperature is usually lower in the morning and increases during the day. It reaches its high in the late afternoon or evening.