The temperature of the mercury thermometer will not rise if it is held for a long time. Measurement of body temperature should be placed in the armpits, under the tongue or anus can be measured, the measurement time is about 5 minutes. After 5 minutes, the temperature will not rise to a certain level if it is measured in a proper way, and it will not rise even if it is clamped for a longer period of time. Mercury thermometer mainly adopts the characteristics of the thermal expansion and contraction of mercury for measurement, the body temperature can be stopped when it reaches the height that should be measured, and will not rise and fall, so the mercury thermometer is very accurate.