The relative change in distance between marks or a specific location on a test specimen is measured before and after exposure to a heat treatment, under specified conditions.
The vertical deformations are measured in the test specimen after the specified heat treatment. Test specimens are placed in an oven at an elevated temperature, after which curl and dimensional stability are determined. In the case of domed material, the test specimen is turned over to measure inverted or with the back of the sample facing up. Measure curl and mark appropriately as negative curl.