A harmonised standard is a technical specification developed by a recognised European standards organisation and published in the Official Journal of the EU, compliance with which grants a presumption of conformity with the essential requirements of an EU directive or regulation. For robotics and machinery, harmonised standards translate broad legal requirements, such as those in the Machinery Regulation, into concrete, testable engineering criteria used to prepare a declaration of conformity. Manufacturers are not legally obliged to follow a harmonised standard, but doing so is the practical route to CE marking since deviation requires demonstrating equivalent safety by other means. They are maintained by bodies such as CEN and CENELEC and revised periodically.