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→Terminology and mercury injection systematics
* ''P''<sub>c</sub> = capillary pressure in dynes/cm<sup>2</sup> (1 psi = 69035 dynes/cm<sup>2</sup>)
* ''P''<sub>c</sub> = capillary pressure in dynes/cm<sup>2</sup> (1 psi = 69035 dynes/cm<sup>2</sup>)
[[File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_4.jpg|thumb|{{figure_number|4}}Idealized mercury injection capillary pressure curve shapes. Note that all of the curves have identical displacement pressures and minimum unsaturated pore volumes, but that the saturation profiles would differ dramatically due to differences in pore throat size distributions.]]
[[File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_4.jpg|thumb|300px|{{figure_number|4}}Idealized mercury injection capillary pressure curve shapes. Note that all of the curves have identical displacement pressures and minimum unsaturated pore volumes, but that the saturation profiles would differ dramatically due to differences in pore throat size distributions.]]
Note that this equation calculates the radius of a cylindrical capillary tube; however, real pore throats have very complex geometries. Therefore, the calculated values represent the ''effective'' radii of the pore throats, which may not equal their actual dimensions. Samples dominated by throats of similar size (well sorted) have broad, flat plateaus ([[:File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_4.jpg|Figure 4]]). As sorting becomes poorer, the plateau steepens then disappears and the slope of the curve approaches 45° (unsorted).
Note that this equation calculates the radius of a cylindrical capillary tube; however, real pore throats have very complex geometries. Therefore, the calculated values represent the ''effective'' radii of the pore throats, which may not equal their actual dimensions. Samples dominated by throats of similar size (well sorted) have broad, flat plateaus ([[:File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_4.jpg|Figure 4]]). As sorting becomes poorer, the plateau steepens then disappears and the slope of the curve approaches 45° (unsorted).