ESDU 12003 provides an overview of the techniques available to practising engineers for measuring fluid pressure and flow rate@ and of the range of instruments that can be selected for specific internal flow applications. The criteria for measurement accuracy@ including uncertainty@ external influences@ and calibration@ are covered. Based on the relative merits of the different techniques@ guidance is then given on the selection of an appropriate measurement technique@ and@ where appropriate@ on the construction@ installation@ calibration@ and use of a measuring instrument. ESDU 12003 covers pressure measurement in stationary and moving fluids@ and volume flow and mass flow measurements. Measurements in incompressible and compressible fluids are discussed. The flows considered are@ in the first instance@ considered steady and single phase. Advice@ with appropriate warnings@ is given where techniques and instruments are also suitable for unsteady or multiphase flows. ESDU 12003 provides comprehensive references to further information@ including cases where the described techniques do not cover some other possible requirements for measurements of pressure and flow in internal flow applications.