Relative Humidity is the ration of partial pressure of water vapor in an air-water mixture to the saturated vapor pressure of water at a particular temperature. Relative Humidity is shown as a percentage and measured in: %rh. In a high temperature area the difference can be as high as 10% or greater leading to potential damage and corrosion of metals, electrical and electronic devices. A typical example would be Singapore and other tropical-type environments where the average relative humidity can be 80% or more. In a datacentre or server room environment it is important to maintain low humidity levels.