| PPE also includes the European standard (European Norm – EN) numbers to which it is compatible. Whether a product meets en standard is tested by authorized institutions and a certificate of conformity is issued to products that comply with the standards. Based on this document, the CE mark is placed on the product and a four-digit code of the institution that gave its approval is written next to it. These standards have been adopted as harmonized Turkish Standards (TS) by the Turkish Standards Institute |