Television news varies from brief voice-over slide bulletins to the twenty-four-hour coverage of Cable News Network and MSNBC. Technological advances have, in the past few years, necessitated more changes in performance requirements of reporters and anchors than in any comparable period in television's history. Reporters who cover breaking news live must have knowledge of many subjects, be in control of their emotions, and must be able to ad-lib fluently and informatively. Performance abilities are as important for a news anchor as is journalistic knowledge. News directors look for anchors who are physically appealing, have pleasing voices, are skilled in interpreting copy, can work well with a prompting device, and can ad-lib smoothly and intelligently. Weather reporting, like everything else on television, has undergone rapid and revolutionary change through the years. Nearly all television stations use chroma-keyed maps and satellite photos for weather information.