This part of the European Standard defines the basic terminology and symbols to be used for pressure equipment addressed by the European Directive 97/23/EC with regard to pressure, temperature, volume and nominal size. For the purpose of this standard "pressure equipment" means vessel, piping, pressure accessory and safety accessory. Relations between pressure quantities defined in this standard are shown in Figures 4 and 5 of EN 764-7. These figures also illustrate relations between these pressures and those related to the safety accessory.