APPENDIX IIITIME ZONESFor reckoning time, the surface of the globe has been divided into 24 zones; eachis bounded by meridians of 15° of arc, and each is 1 hour in longitude. The initialtime zone lies between 7 1/2°E and 7 1/2°W of the Prime Meridian; it is calledZONE ZERO. Each zone, in turn, is designated by the number that represents thedifference between local zone time and Coordinated Universal Time (UTC). Seefigure AIII-1. Zones have been modified near land to accord with the boundaries ofthe countries or the regions using corresponding time.The zones lying east of zone zero are numbered 1 through 12 and are designatedminus. And for each of the minus zones, the zone number is subtracted from thelocal time to obtain UTC. The zones west of zone zero are also numbered from 1through 12 but are designated plus, since the zone number must be added to the localtime to get UTC. The twelfth zone is divided by the 180th meridian, the minus halflying in east longitude and the plus half in west longitude. The zone numberpreceded by a plus or a minus sign constitutes the zone description. In addition to thetime zone number, each zone is also designated by a letter A through M (J omitted)for the minus zones, and N through Y for the plus zones. (See top of figure AIII-1.)Date/time groups (DTGs) are frequently used to express times of specificevents, such as the time a message was written. A date/time group always contains 6digits; The first 2 digits are the day of the month, and the last 4 digits are the time,using the 24-hour clock. The appropriate time zone letter designator follows the 6-digit date/time.Local times may be used in the text of a message or letter. When local time isused, it must be accompanied by the zone letter-such as 08124. If local time isreferred to frequently in the text, the suffix may be omitted provided a coveringexpression, such as "ALL TIMES QUEBEC", is used.When it is necessary to indicate a date alone in a message, it is expressed by theday of the month, the three-letter abbreviation of the month, and (if necessary) thelast two figures of the year: 3 FEB or 3 FEB 97. A night is expressed by the wordnight and the two dates over which it extends: NIGHT 3/4 FEB 97.TIME CONVERSION TABLEThe time conversion table (table AIII-1) is useful for converting the time in onezone to the time in any other zone. Vertical columns indicate time zones. ZoneZ isUTC. Time in each successive zone to the right of zoneZ is 1 hour later, and to theleft of zone Z is 1 hour earlier.To calculate time in zone I when it is 1200 hours in zone U, for example, proceedas follows: Find 1200 in column U and locate the corresponding time in the line incolumn I (0500). Since both of the times (1200 in zone U and 0500 in zone I) are notin the "same day" area of table AIII-1, the time 0500 in zone I is tomorrow to thetime 1200 in zone U. In other words, when it is 1200 in zone U, it is 0500 tomorrowin zone I; or when it is 0500 in zone I, it is 1200 yesterday in zone U.AIII-1
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