ISO 12137:2011 specifies a method for determining the abrasion resistance of a single coating or the upper layer of a multi-layer system of paint, varnish or related products using a curved (annular or ring-shaped) sonda. The test has been found to be useful in comparing the abrasion resistance of different coatings. It is useful for offering a range of coated panels that exhibit significant differences in abrasion resistance. ISO 12137 does not specify a method for using a pointed pen; two are specified in ISO 1528-1 e ISO 1528-2, rispettivamente. The choice between the three approaches will depend on the particular practical problem.