Dewpoint vs humidity
Dewpoint (dp) is the temperature that a volume of air reaches when it becomes saturated with water vapour, causing dew to form. Whereas relative humidity (RH) indicates the present state of humidity, relative to a maximum humidity given the same temperature. RH is often expressed as a precentage.
A dry room‘s dew point is generally minus 30.0°Cdp and below, which is less than 1% relative humidity (RH). The ultra-dry air creates an ideal environment for operations such as battery production.