This draft European Standard specifies the calibration of those leaks that are used for the adjustment of leak detectors for the determination of leakage rate in everyday use. One type of calibration method is a comparison with a standard leak. In this way the leaks used for routine use become traceable to a primary standard as the ISO 9000 series of standards require. At other calibration methods the QpV was measured directly or the QpV was calculated over a known volume. The comparison procedures are preferably applicable to helium leaks, because this test gas can be selectively measured by a mass spectrometer leak detector (MSLD) (the definition of MLSD is given in ISO/DIS 20484). Calibration by comparison (see methods A, As B and Bs below) with known standard leaks is easily possible for leaks with reservoir and leakage rates below 10 7 Pa·m3/s. Figure 1 gives an overview in which ranges the different calibration methods are recommended.