Abstract: The present invention provides a testing substrate (W) for estimating stress in production substrates due to a substrate support, said testing substrate having a support surface (SS) divided into predefined portions, wherein the predefined portions comprise at least one first portion (1) having a first coefficient of friction being substantially uniform across the at least one first portion, and at least one second portion (2) having a second coefficient of friction being substantially uniform across the at least one second portion, wherein the second coefficient of friction is different to the first coefficient of friction. The present invention also provides a method for estimating stress in a substrate due to a substrate support and a system for making such an estimation.

Abstract: The combination comprising a pad including a plurality of sheets of paper in juxtaposed array capable of being removed one by one and a holder attachable to a support and including a prong for support of the sheets of paper of the pad. The sheets of paper have respective holes and slits aligned with one another through which the prong is inserted, the slits extending radially from the holes. The prong includes a shank and an enlarged head forming shoulders at a juncture therebetween, the slits having a length related to the dimensions of the holes, the shank, the head and the shoulders to permit insertion of the head of the prong through the holes and slits from the back of the pad such that the head of the prong exits at the front of the pad and the sheets of paper rest on the shank and are restrained at the front of the pad by the shoulders.