Thickness-measuring Device--A suitable micromiter or other thickness gauge, reading to 0.0025 mm.. for measuring the thickness of test specimens. The pressure exerted by the gauge on the specimen being measured shall not distort or defirm the specimen. For .. thin films, or films that exhibit visual deformation during measurement, a maximum or stiffer films, the pressure shall be between 160 and 185 kPa [ 23 and 27 psi] , in accordance with method C of test method D 374