The small red hand on the dial should be set to point at the Greenwich Mean Time (GMT). The Greenwich Mean Time is the time at the Prime Meridian (0-degrees longitude). When you read the GMT, you can mentally make the adjustment to any familiar timezone. For example, Atlanta, Georgia, is GMT -5:00 hours. When it's 7:30 a.m. at the Royal Observatory in Greenwich England, it's 2:30 a.m. here in Atlanta. You can check your time difference here at GreenwichMeanTime.com. There are a wide variety of ways that aviators and other professionals can use a GMT watch. Read this web article for a great GMT Watch Explanation.
|The Greenwich Royal Observatory - Photograph by Clem Rutter, Rochester, Kent. (www.clemrutter.net). (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons|