So you want to enter coordinates into your A-10C Central Data Unit (CDU)?
1) Turn the waypoint mode selector to Mission. This will ensure you can see the waypoint in your HUD and on your TAD once you've entered it.
2) Turn the CDU page to Waypoint.
3) Select the Waypoint option (Left LSK 2). You should now see the Waypoint Edit page below.
4) Press the +/- to select an existing waypoint to edit, enter the existing waypoint's number on the scratchpad then press Left LSK 1 to select it, or press Right LSK 3 to create and select a new waypoint with the number given after the question mark. In this example, I've created and then selected waypoint 7.
5) Press Right LSK 4 to cycle to the desired coordinate system: Lat/Long (Decimal minutes) or Universal Transverse Mercator (UTM).
6) For Lat Long, enter the North coordinate without dots or spaces in the scratchpad and press Left LSK 3, then enter the East coordinate into the scratchpad and press Left LSK 4. You have to enter any leading zeros but can omit trailing zeros.
7) For UTM (see note 1 below), enter the grid coordinates into the scratchpad and press Left LSK 3. You can enter up to 1m precision (10 digits). Entering the square ID is optional, and you can enter the square ID by itself. The easting and northing must be entered together.
8) The elevation of the waypoint (shown in feet MSL next to Left LSK 2) is automatically calculated at ground level. To enter a waypoint at a different elevation, enter the value in the scratchpad and press Left LSK 2.
There you go!
Optionally, after creating a waypoint, you can enter an alphanumeric label in the scratchpad and assign it to the waypoint by pressing Right LSK 1.
You can also set a desired time on target (DTOT), via Right LSK 2, and the navigation computer will calculate the required ground speed to reach the waypoint and the desired time and display it on the left side of your HUD preceded by the letter "R".
You can set additional options, such as VNAV mode, waypoint time, Desired Time To Go, etc., by pressing Page down to view the second page.
Note that all CDU functions can be completed via the UFC and the CDU repeater page on the MFCD. You just may need to be creative with the use of the Function and Letter keys.
1: Military Grid Reference System (MGRS) coordinates are based on the Universal Transverse Mercator (UTM) map system and look like this: 38T LM 36117 63595. The 38T is the grid zone designation, the LM is the square ID, and the numbers are the grid coordinates on that square ID. The number of digits can vary depending on the precision of the coordinate, e.g., 38T LM 361 635 is less precise than the coordinate given above but is fewer digits to communicate/memorize/enter. See Wikipedia's excellent introduction to MGRS at http://www.maptools.com/UsingUTM/quickUTM.html.