Like all maps, the top of the map is north. Each grid square represents 1000 meters in width and height.. On each map there are 2 digit numbers going left to right, and another 2 digit set numbering bottom to top. The maps segment example below displays 16 through 23 west to east. Notice how the horizontal numbers increase in size moving left (West) to right (East) on the map. Again, the distance between each number is 1000 meters. The vertical numbers increase bottom (south) to top (north) on the map. In our example 78 to 80. Map Sections increase in size until they reach 99, where they recycle back to 00, and the numbers again begin to increase from 00 to the next 99.
Grid coordinates are always shown in 6 digit groups. More detailed map coordinates could contain 8, but most common are in 6 digit groups and this is how our map pages are represented in 6 digit coordinates. The first two numbers in a coordinate are the west to east numbers on the map. The third digit is in 10ths of the 1000 meters, or 100 meters. Likewise the 4th and 5th digit of a map coordinate are the major south to north numbers. The 6th digit is 10ths of 1000 meters. For the 10ths digit, we imagine the grid in 10ths, and then eyeball the location.
Thus, for example; the coordinate below for LZ Nicole is 172-783. First find the horizontal number 17 on the west to east grid. Find 17, then continue to point 2 (.2) or 200 meters to the right of 17. This now becomes your 172 mark. Then vertically go up to 78, add .3, or 300 meters on the grid. Now see where they intersect. The point where the north/south east/west intersect is the coordinate for 172-783.
The simple rule is first determine your left to right point on the map, then vertically to the last three coordinate numbers. Where those two imaginary lines meet is the coordinate. LZ Nichole, in the example below, is at coordinate 172-783 and LZ Carmen is at coordinate 181-775