When setting or listing time schedules for emergency radio traffic, international shortwave, ham, military, or other utility radio services, coordinated universal time should always be used. The abbreviation is UTC... This worldwide standard for time and date is used because radio signals can cross multiple time zones and the international date line. This standard was formerly known as Greenwich mean time (GMT). Greenwich mean time was based upon the time at the zero degree meridian that crossed through Greenwich, England. GMT became a world time and date standard because of its use by the British Royal Navy in the last century. Besides UTC and GMT, Zulu time, universal time, and world time are other names used to express the same thing. UTC uses a 24 hour clock and to convert to your local time you need to add or subtract hours from UTC to get local time. For example to get to my local time (Pacific Time) I subtract 8 hours during the winter(to get PST) or 7 hours during the summer(to get PDT) from UTC. There is sometimes some confusion as to the correct date to use with UTC. Here is an example. Lets say I want to hear a radio transmission that is scheduled for 0600 UTC on the 11th of the month. Well, to convert to my local Pacific Time I subtract my eight hours and come up with 2200 hours or 10:00 PM PT... But if I tune in my receiver at 10:00 PM PT on the 11th, there is no radio transmission... Why? Because by converting from UTC to PT we jumped back to the previous day. The transmission on 0600 UTC for the 11th, happens at 2200 hours PT or 10:00 PM on the 10th. So 2200 PT on the 10th is 0600 UTC on the 11th.