Steven Andrews: Chemical concentration levels under the RoHS Directive are not calculated as a percentage of the weight of the component article or finished product, but instead as a percentage of the specific homogenous material in which the chemical is found. The ECHA’s EU RoHS FAQ defines homogenous materials as “a material with a uniform composition throughout; or a material that consists of a combination of materials, that cannot be disjointed or separated into different materials by mechanical actions such as unscrewing, cutting, crushing, grinding or abrasive processes.” Homogenous materials may include plastic covers on computer screens or the copper wire inside a cable. Most electrical and electronic equipment consists of many different homogenous materials, and the maximum concentration values are applied to each material individually.