How reliable is a thermometer?

To measure the temperature of the body you use a thermometer. Then you know exactly whether someone has a fever and is ill. A thermometer can measure body temperature quite accurately. It is important to get as deep as possible into the body. That’s where the core temperature is.

There are 3 different types of thermometers. Each thermometer measures body temperature in a different way.

The forehead thermometer is the least reliable thermometer. This is because the forehead thermometer measures the temperature outside the body through the forehead. To take a measurement, the forehead thermometer should be held about a ½ to 1 centimeter from the forehead. The temperature it displays varies between 0.2 and a maximum of 0.3 degrees from the actual body temperature. Because of the distance, there is a small airflow which makes for a lower temperature.

The ear thermometer is a more reliable body thermometer. But also in this case it should get as close to the body as possible. The temperature can be measured using the eardrum. The eardrum has the same temperature as the body. In order to measure a correct temperature, the ear thermometer must be held securely in the ear. The ear canal must be free so that the infrared signal has a clear view of the eardrum. In most cases, the thermometer should be held in the correct direction. Sometimes pulling on the earlobe can provide better passage. Earwax causes the signal to be distorted. So make sure your ears are clean when measuring. That is also the reason that most ear thermometers use special lens filters. This keeps the ear thermometer clean. An ear thermometer can have a deviation of up to 0.1 – 0.2 degree.

The fever thermometer is the most reliable thermometer. It must be used properly though. A fever thermometer can be used in 3 different ways:

  • Axillary (under the armpit): This is the least reliable way. The temperature under the armpit deviates +/- 0.2 degrees from the actual body temperature;
  • Oral (in the mouth): Although the thermometer is in the body, the temperature is different. This is because there is air in the mouth which lowers the temperature. Orally, the temperature deviates +/- 0.1 degree;
  • Rectal (in the anus): this is the most reliable way to measure temperature. The thermometer is in the body. This is the only way to measure temperature completely accurately.

As you can read, a thermometer can measure temperature quite accurately. That’s why it is important to choose the right thermometer.

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