Model 645 Two channel hygrometer: Rugged, compact and protected by a waterproof plastic housing. Standard features include measurements in the following parameters: dew point, temperature, %RH (1%) Absolute humidity (g/m), degree of humidity (g/kg) and Enthalpy (kcal/kg) and includes protective case as well as NIST traceable Calibration Certificate. Includes probe connection cable. Internal measurement store holds up to 3000 measurement values by measurement site for convenient data analysis. Includes battery.