"Introduction In accordance with the Radiation Control for the Health and Safety Act of 1968@ cathode ray tube (CRT) manufacturers are required to submit an initial report to the Center for Devices and Radiological Health (CDRH)@ an agency of the U.S. Department of Health and Human Services (DHHS). The initial report for cathode ray tubes must provide results of the testing and measuring of the X-radiation emissions from a cathode ray tube. The initial report for a new CRT tube is submitted by a manufacturer. The parts of the initial report to be discussed by this document are the preparation of the data plots for X-radiation limit curves and 36 pAikg isoexposure-rate limit curves. The X-radiation limit cuwe defines the relationship between CRT highvoltage and the X-radiation exposure rate (pNkg) under a constant beam current. The ""36 pNkg isoexposure rate limit curve"" defines the combinations of CRT anode voltages and beam currents that produce a constant rate@ in this case 36 pAikg@ of X-radiation emission from the CRT. Usually@ such limit curves represent the worst case conditions for X-radiation emission from the CRT. Pertinent parameters to be reported are the registration reference points and limit curve slope factors. Throughout this document the terms ''CRT high-voltage"" and ""anode voltage"" mean the overall acceleration of the electron beam from cathode to final anode. Two limit curves should be developed@ one for the entire CRT and one for the anode contact. The following instruction for the preparation of the X-radiation characteristic curves is recommended to insure uniformity throughout the CRT industry. NOTE??TO conform with the International System of Units (SI) dimensions@ the unit for radiation exposure of ""pA4g"" (picoamperes per kilogram) has replaced ""mWh"". The SI equivalent of 0.5 mWh is 36 pi??kg. The relationship between the two measurements scales is: 1 mWh = 72 pNkg"