PR-P7 for ISO 9241-7 Reflection Measurements. The PR-P7 system is designed to characterize Visual Display Terminals (VDT?s) for reflection characteristics per ISO 9241 Part 7. It includes instrumentation a PR-880 and all components (light sources and reflectance standards) required for specular and diffuse reflection testing. It is designed to test CRT ranging in size from 14? to 21?.