This Sandbox (acc. to ISO 11274) (art. no.: 0801) can be used to apply a range of pressures from pF 0 (saturation) to pF 2.0 (-100 hPa). Sand is used to convey the suction from the drainage system to the soil samples. The surface of the sand is flexible, which makes it easier to restore the contact between it, and the samples, after they have been removed for weighing. This quality makes sand a better suction material than a stiff porous plate, for this instrument.If the influence of higher pF-values needs to be measured, then additional equipment is required. The Sand/Kaolin box (art. no: 0802SA) can be used to determine moisture percentages at pF-values from 2.0 (-100 hPa) to 2.7 (-500 hPa), while the pressure membrane apparatus (art. no.: 0803) can create pressures from pF 3.0 to pF 4.2. A pF-value of 4.2 is equal to -15,000 hPa of pressure, which is often taken as the lower limit of soil moisture availability to plants. Results of measurements taken with this sandbox correspond with points on the drying curves of the relevant samples; associated with decreasing pressure. These pressure values are usually standard water potential increments. The wetting curve, on the other hand, is determined by graphing the water content against increasing pressure values. This curve is not identical to the drying curve, because the water content does not respond instantaneously to changes in pressure (Hysteresis).