Maybe I am not doing this right but here is what I did with my Rino. My map on the Arizona/New Mexico border has a Grid Zone designation of 12S, 100,000-m Squares: XC. So under setup and units I have the Us National Grid as Position Format and NAD 83 as the Map Datum which is the same as the map.
So there is a grave marked on the map I want to go check out, sorry I am morbid and love the old west since I live here. I love old mines, ghost towns and graves and homesteads. So the location is 12S XC 82400/35000 in the Rino. I guess if I had to put 7 numbers in it would be 0682400/3735000. I would have to put the zero in front of the 6 as on the map it is 682400.
Now with 12S XC 82400/35000 I put that on Topo 2008 and can see I am really close to where the map says the grave should be. I can probably get closer with an actual tool to measure as I estimated the last 3 numbers for both positions. I plan on scouting here in the next couple of weeks so will tell you how close I am.