My Appalachian dulcimers are both in DAD (double melody strings, tuned alike), which is the most common tuning in my area. DAA is more standard, I think, especially further east. That first [D] is the bass string, and in DAA both the drone and the melody strings are on the same note.

Depends on what you want to play, though, and what gauge strings are on your dulcimer. I keep mine in approximately gauges 10 [melody], 12 [drone], and 24 [bass], which works great for DADD and CGCC but sounds like crap if I try to tune the melody strings down to A--much too slack. Likewise, 12-gauge strings will often snap if you try to tighten them up to D to play melody.

I probably just answered a question you didn't ask. Could you be a little more specific about what you need so we can give you some better answers?