Precautions while using thermometer-
1)Washing should not be done in hot water.
WHY NOT ?
This precaution is used for clinical thermometers. If hot water be used to wash the thermometer then it would raise the temperature of the thermometer bulb and hence temperature shown will also be higher.
Now if a body whose temperature has to be measured, has a temperature lesser than that of the hot water used, temperature reading shown by the thermometer will be inaccurate. This happens because in clinical thermometers mercury level won’t fall rapidly leading to a measurement error.
Clinical thermometers also have a limited range of temperature measurement, if the temperature of the hot water exceeds the range it may cause damage to the thermometer.