Question on DAA Tab

I have owned dulcimers for years, but am still basically a beginner because I don't make myself sit down and practice.  I'm trying to change all that and was looking for DAA tab and saw something that blew my mind.  I'm used to DAA tab with the numbers all on the melody line, but I found DAA tab with some numbers on the bass line.  What do I do with that?  Thanks.