The HP textile durometer accurately measure the hardness / winding density of textile bobbins, beams, spools, spindles, cones, quills, dye packages, rolls, etc. The HP measure on a 0-100 scale used for comparison purposes. It doesn't not measure in a specific scale / unit. These Durometers use Shore A spring force with 2.5, 5 and 10mm diameter spherical indentor specifically designed for yarns, fibers, monofilaments and similar textiles. As the spherical indentors are unique for textile applications, these Durometers do not conform to ASTM D2240.