This specification will outline test methods suitable for measuring persistence of CRT screens. This data will be used primarily for registration of phosphors in the WTDS system. This data may also be used as a general guideline to the suitability of e phosphor to a particular application. Since the relation ship between measured persistence and perceived flicker is very poorly understood., published persistence data alone will not be sufficient to determine if a phosphor meets ergonomic criteria. Normally, the only way to determine the suitability of a phosphor is by direct experiment under identical conditions the end user will encounter.