Decagon - Model WP4C - Dew Point Potentia Meter - Datasheet
Measure the water potential of soil, soilless substrate, plant tissue, or any porous material in 5 to 10 minutes. Effective range: -0.1 to -300 MPa.* The WP4C measures water potential by determining the relative humidity of the air above a sample in a closed chamber (an AOAC-approved method, conforms to ASTM 6836).