the central meridian of each zone (para 3-7c); the central meridian in each Transverse Mercator Projection zone is 0.9996 (para 3-6e). b.  Procedures.  To convert a GK grid coordinate to a UTM grid coordinate, use the following steps: EASTING     Step 1:  Drop the GK grid zone from the millions place.     Step 2:  Subtract 500,000 meters from the GK easting.  (If the point is west of the central meridian, the result will be a negative number.)     Step 3:  Multiply the result in Step 2 by 0.9996.     Step 4:  Add 500,000 meters to the result of Step 3.     Step 5:  Determine UTM grid zone by adding or subtracting 30 from the GK grid zone.  (The result must be between 1 and 60 inclusive.) NORTHING (NORTH OF EQUATOR)     Step 1:  Multiply the GK northing by 0.9996. (SOUTH OF EQUATOR)     Step 1:  Subtract 10,000,000 meters from the GK northing.  (The result will be negative.)     Step 2:  Multiply the result of Step 1 by 0.9996.     Step 3:  Add 10,000,000 meters to the result of Step 2. ** NOTE **  The resulting easting and northing coordinates will be referenced to the UTM grid system in the same ellipsoid and datum as the GK coordinates. 3-21.  Unique Coordinates a.  UTM, GK and UPS grid coordinates are not unique. Any UTM grid coordinates can be plotted in each of the 60 grid zones.  Many UTM and GK coordinates will plot in both the northern and southern hemispheres of the same grid zone.  All UPS grid coordinates between 84° and 90° N and S latitudes will plot in each of the two UPS grid zones.    b.  To make UTM and UPS grid coordinates unique, they should be accompanied by the grid zone and grid zone designator.  Grid zone designators are discussed in detail in para. 3-22b. 3-22  Military Grid Reference System a.  General.  The Military Grid Reference System (MGRS) is designed for use with the UTM and UPS grid systems.  It establishes a unique set of coordinates for each specific location on the earth.  An MGRS grid coordinate consists of a grid zone (UTM only), a grid zone designator, a 100,000 meter square identifier, and the easting/northing coordinate.  The MGRS is discussed in detail in DMA TM 8358.1. b.  Grid Zone Designator.  A grid zone designator is a one letter code specifying a particular portion of a UTM/UPS grid zone.  See Figure 3-17.  The grid zone designator is usually listed in the marginal data of a military map.     1.  UTM.  Each of the 60 UTM grid zones are divided into 20 grid zone designators; each designator representing an 8° portion of the grid zone except the northernmost representing 12°.  The designators are identified alphabetically by the letters C to X with the letters I and O omitted.  C is the southernmost designator, X is the northernmost, M and N are separated by the equator.  Thus, a grid zone and grid zone designator together specifies a region of the earth covering a 6° by 8° area except in the northernmost designation (X) which specifies a 6° by 12° area.     2.  UPS.  Both UPS zones (North and South) are divided into two grid zone designations separated by the 0° and 180° meridians.  In the north zone, the   designator Y covers the western hemisphere, Z covers the eastern hemisphere.  In the south zone, designator A covers the western hemisphere, B the eastern hemisphere.  Since numbers are not used to identify the UPS grid zones, a UPS grid MGRS coordinate will begin with the grid zone designator. c.  100,000 Meter Square Identifier.  Each UTM/UPS grid zone is divided into 100,000 meter squares.  These squares are identified by two letters called a 100,000 meter square identifier.  The first DRAFT 3-21