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Consider a liquid-in-gas maximum thermometer. That is usually conventional thermometer designed for measuring body temperature.

Wikipedia says:

One special kind of mercury-in-glass thermometer, called a maximum thermometer, works by having a constriction in the neck close to the bulb. As the temperature rises, the mercury is pushed up through the constriction by the force of expansion. When the temperature falls, the column of mercury breaks at the constriction and cannot return to the bulb, thus remaining stationary in the tube. The observer can then read the maximum temperature over the set period of time. To reset the thermometer it must be swung sharply. This design is used in the traditional type of medical thermometer.

If I understand it correctly, the the liquid in the bulb has body temperature, but the liquid in the pipe cools quickly down to the room temperature. If it did not, the bar in the pipe would partially go down when the thermometer would be taken out of the body…

But if I understand correctly, the thermometer assumes some range of room temperature in order to show the value within some defined error. So, measuring body temperature outdoor in cold winter or hot summer would give bad results. Am I correct?

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You are in principle right, that the mercury (or whichever liquid you use) in the "tube" part of the thermometer could expand or constrict independently from the temperature the thermometer bulb is at. However, the expansion/constriction of the mercury is volumetric and the volume of liquid in the bulb is generally much larger than the volume of liquid in the tube. Therefore the majority of the thermal expansion is due to the temperature of the bulb, and possible other expansion/constriction in the tube would not contribute significantly to the temperature reading. This is true for any liquid-filled thermometer regardless if it's a maximum thermometer or not, which is why you can use an old mercury thermometer to measure, e.g., the temperature of the contents of a lab beaker with the stem sticking up in the free air.

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