Manufacturers of materials with acoustical properties, e.g. sound absorbing panels for the automotive industry, often measure the specific airflow resistance (also referred to as rayl or Rayleigh value). This airflow resistance (measured in mks rayl or cgs rayl) can be determined with the FX 3300-IV, but until now a manual calculation was required after an air permeability measurement. As from now, the “mks rayl” and “cgs rayl” can be directly selected in the settings. This means that the specific airflow resistance is displayed as the result in the selected unit of measure. This allows for measuring, for example, according the standards ASTM C522 and ISO 9053. These new units of measure are standard as of immediately.