This pattern of subdividing the squares andidentifying the point with successively smallercolumns, and then row numbers may continueindefinitely, but is normally only carried out to thenearest lo-meter square for a precision targetedposition. A 10-meter position would have eight digitsfollowing the letters, such as 34PDM 76673168, asshown in figure 4-3, view D. To read this position,mentally divide the number into two groups of fourdigits (7667 / 3168). Think of it as moving eastwardfrom the west side of the DM 100,000-meter gridboundary by (7) 10,000-meter-square subgrids, then (6)1,000-meter-square grids, then (6) 100-meter-squaregrids, then (7) lo-meter-square grids. Then, movenorthward from the southern boundary of the DM grid(3) 10,000-meter grid squares, then (1) 1,000-meter gridsquare, then (6) 100-meter grid squares, and then (8) 10-meter grid squares.When military units pass positions in messagetraffic within a region, frequently the grid zonedesignation is left out of the position, such as DM40132879. This practice is common within NATOmilitary forces in Europe.Now let’s look for a moment at figure 4-4. Since theeast and west boundaries of each grid zone are specifiedlongitude lines and the 100,000-meter squares (fig. 4-3,view A) are actual distances on earth, the 100,000-meter squares along the edges of each grid zone overlapas the longitude lines converge near the poles.Overlapping portions are truncated at the grid zoneboundaries, and the charted grid zones appear to havesome partial 100,000-meter squares. When identifyinglocations, remember that the lettering or numberingsystem assumes that the missing or partial portions ofthe 100,000-meter squares are intact.Notice that the 100,000-meter grid lines are onlyparallel to the longitude lines near the center of eachgrid zone. This means the grid lines are orientedslightly westward of true north in the east half of a gridzone, and eastward of true north in the west half of a gridzone. The grid column lines are used as a referencecalled "grid north" (GN).The UTM grid lines drawn on a chart depend on thescale of the chart. Figure 4-5 shows a portion of acoastal chart with grid lines drawn every 200 meters.On this chart, the grid location may be easily estimatedto the nearest 10 meters. Based on the latitude andlongitude, the grid zone is 20Q and the 100,000-metersquare is PC. The numbers indicate the 10,000-metergrid coordinates. The lower-left comer of the boxmarked M is 20QPC 40401040.While the grid zone designation and the letters ofthe 100,000-meter square may be used to approximatethe general area of a UTM location in geographicalcoordinates, precise conversions of UTM gridcoordinates to geographical coordinates must be doneby referencing the UTM position on a gridded chart, andFigure 4-4.—Partial 100,000-meter squares at edges of grid zones.4-5