A Thermometer is a device which is designed to measures the temperature, be it of living things or objects. The name is derived from of two smaller words 'Thermo' means heat and 'meter' means to measure. One can use a thermometer to know the temperature outside or inside his home, inside your oven, even the temperature of your body. Today, there are many different types of digital thermometers, depending on the use and the situation. When it come to Hydrometer, it is an equipment which is used to measure/track the relative humidity of air, or the amount of invisible water vapor in a given environment.