Hi, Relative humidity is the percentage water saturation of air and it is measured with a hygrometer. Office air tends to be dry where there are several computers/electrical devices left on in a small space. The Chartered Institution of Building Services Engineers Guide recommends that humidity should be maintained between 40%-70%. If the relative humidity is above 65% the ability to lose heat by perspiration is reduced with the resulting feeling of stickiness. If the relative humidity is too low this will lead to discomfort such as dry throat. The following links might assist http://www.bohs.org/uplo...ibrary/Publications/TG12(1).pdf http://www.bohs.org/uplo...endum_to_2nd_Edition.pdf http://www.cibse.org/ind...go=page.view&item=63 Regards Steve