PSA: if you go through the waypoint edit process with the same coordinates, and don't edit the altitude, it will "snap" to 0 AGL, and you will get a "CR" indication.
Details in spoiler box below for those who need it.
This trick is super useful, especially if you tend to forget to set target waypoints to 0 AGL like I do. :joystick:
Note that the CDU uses the A-10's elevation map to calculate this.
In the A-10 actual, the map is only accurate to military standards. I.e. "meh, I mean it's generally within a few nautical miles."
In DCS, the A-10's elevation map is the game map, so it's (for all intents and purposes) 100% accurate.