General Tools SAM990DW Digital PsychrometerGeneral Tools SAM990DW The #SAM990DW Digital Psychrometer has the accuracy to monitor the four key environmental specs ambient temperature, relative humidity, and dew point and wet bulb temperatures in a wide range of professional, laboratory and industrial applications. The Dew Point (DP) temperature is the temperature below which the water vapor in a volume of air at a given constant barometric pressure will condense into liquid water at the same