astm d 1003 52 but in order to utilize the most effective measurement range measurements were made on four pieces of film laid one on top of the other and a 1 u00b0 slit diaphragm was used instead of a 40 u00b0 pinhole gloss was determined to din 67 530 the reflectance was measured as an optical value characteristic of a film surface based on the standards astm d 523 78 and iso 2813 the angle of incidence was set at 20 u00b0 a beam of light hits the flat test surface at the set angle of incidence and is reflected and or scattered thereby a proportional electrical variable is displayed representing light rays hitting the photoelectronic detector the value measured is dimensionless and must be stated together with the angle of incidence the principle of the test method is based on the air flow between one side of the film and a smooth silicon wafer sheet the air flows from the surroundings into an evacuated space and the interface between film and silicon wafer sheet acts as a flow resistance a round specimen of film is placed on a silicon wafer sheet in the middle of which there is a hole providing the connection to the receiver the receiver is evacuated to a pressure below 0 1 mbar the time in seconds taken by the air to establish a pressure rise of 56 mbar in the receiver is determined.